Transits of Venus: New Views of the Solar System and GalaxyInternational Astronomical Union

History of Jeremiah Horrocks

printable versions: pdf, ps

Extracted from course notes for Great Astronomers in History
Distance Learning course, Centre for Astrophysics
by Paul Marston
©University of Central Lancashire

Jeremiah Horrocks

Jeremiah Horrox[1] possessed one of the most original minds of the seventeenth century. A follower of Tycho, Horrox combined a gift for instrumentation with a theoretical genius that later won the acclaim of Hevelius and Flamsteed. His contributions to the lunar theory were the first significant advances on the subject since antiquity, and earned the praise of Newton himself in the pages of Principia.

Allan Chapman[2]

Jeremiah Horrocks

The first observed Transit of the Planet Venus predicted & observed by Jeremiah Horrocks, 24th November 1639
Artist: J. W. Lavender 1903
Image provided by Astley Hall Museum & Art Gallery, Chorley

Gloriana, Elizabeth I, died in 1603, and James VI of Scotland became James I of England. This first Stuart monarch incompatibly combined autocratic royalist views with a Protestantism that was instinctively Presbyterian. The peculiarly English brand of Protestantism had begun with Henry VIII, and settled under his daughter Elizabeth. As James travelled to England in 1603, he received a petition from about 1000 ministers, asking for a conference to decide on church reforms. They objected to the sign of the cross in baptism, wanted less liturgical music, no bowing at the name of Jesus, no profanation of the Lord’s Day, reform of church courts and various other things. In January 1604 James himself chaired the resulting Hampton Court Conference. Most of the “Puritan” demands were rejected, though James did agree to some liturgical changes, and also agreed to authorise a bible translation from which came the “King James” version of the Bible in 1611.

James died in 1625, and his son Charles I was crowned. The House of Commons was now dominated by “Puritans” who advocated extempore prayer and preaching in Anglican churches, whilst the king favoured the “High Church” party, which stressed the value of ritual and prayer book. Charles promoted William Laud to be Archbishop of Canterbury, and he encouraged reintroduction into churches of stained glass windows, crosses, railed altars, bowing at the name of Jesus, and making the sign of the cross in baptism – all things Puritans hated! The king was also in conflict with Parliament over the conduct of various continental wars. From Autumn 1641 the tensions between King and Parliament were rising, and the civil war started in September 1642. Royalist forces dominated in the North and the South West, but also in Oxford. The rise of the New Model Army in 1645 led to Royalist defeat in 1647, and eventually the execution of the still-intriguing king in 1649. The Commonwealth then ruled until the Restoration with Charles II in 1660.

In the England of the early seventeenth century there was little of the strong traditions of astronomy in continental centres like Cracow, Venice, Padua or Bologna. Francis Bacon (1561-1626) was writing to encourage the development of science and scientific communities – but this was a vision not a reality. Bacon’s almost exact contemporary Thomas Harriot (1560-1621) was one of few who sprang to his mind in seeking to further his projects. [3] Harriot was interested in a whole range of scientific issues, including making of lenses that he was using to make telescopes at the same time as Galileo. He was viewing the moon through one on 26th July 1609, three weeks before Galileo showed his to the Venetian Senate, and he was one of the first to observe and study sun spots. He did this in great detail though apparently left no theory about them. Harriot received patronage from various nobles (including Raleigh), but held no academic post. William Gilbert had published his influential work on magnetism in 1600, and (like Harriot, Digges, and the ther small number in this set) favoured Copernicanism. None of these, however, were involved in Keplerian type mathematical astronomy. The universities generally neglected science and astronomy not so much from hostility (there is no evidence of any religious threat to Copernicanism for example) but indifference. It was not part of the curriculum, and if students were interested in it this was as a hobby or pastime. This changed a little in 1619 when a Chair of astronomy was founded at Oxford (more traditionally a science centre than Cambridge), but there was still none at Cambridge.

In religion Cambridge was, of course, exclusively Anglican, and Oxford and Cambridge were the training centres for future ministers in the Church of England which itself (as noted above) was generally Puritan in sympathy – this continuing throughout the civil war and even after the Restoration.[4]

Horrocks’s Life

Details of Horrocks’s brief life are scant and sometimes uncertain. He died on January 3rd 1641, and Dr John Wallis, who entered Emmanuel College with Horrocks and edited his Opera Posthuma in 1673, says that he was in his twenty third year. However, Horrocks matriculated at the University of Cambridge on 5 July 1632, and for this he had to be fourteen according to the regulations. His birth was therefore between January and July 1618.[5]

His family home was at Toxteth Park, now a suburb of Liverpool but then a country hamlet of some two dozen houses with an area called “Otterspool” (heigh ho!). It was once believed that his father was a farmer William Horrocks and such a man did indeed live in Toxteth [6], but the evidence points more to his father as James Horrocks, a watchmaker. The main evidence for this is a remark made by Horrocks’s friend William Crabtree (1610-1644[7]) in a letter to William Gasgoigne (1612-1642) that Jeremiah’s father “died May 3, 1641, grief for his son hastening his own death.” Flamsteed (the first Astronomer Royal) transcribed this letter in the 1670’s, and the Bishop’s transcript records the burial of a James Horrocks of Toxteth on May 4th in St Nicholas Church, at the Liverpool pierhead. Unfortunately the baptismal records at this church for 1618 (the probable year of Horrocks’s birth + christening) are missing. There is also a possibility that the family had come originally from the Deane district of Bolton, where some have suggested Jeremiah was born. A Jonas Horrocks was baptised in Bolton in 1622 – and Jeremiah refers to a brother Jonas of whom there is no other record.[8] Assertions of his birth in Toxteth were made in the 1832 Emmanuel College register itself, in 1859 by fellow Emmanuel student John Worthington (who later preserved his papers), and in 1773 by Emmanuel Fellow George William Bennet in a register of students in 1773 referring to Horrocks as a “very curious astronomer”. Toxteth therefore seems the almost certain birthplace.

The actual place of his birth and childhood is a subject of some dispute. Toxteth Park was a former deer park, and had two lodges when it was de-parked in 1591. By the first years of the 17th century some twenty houses and a couple of mills had been built, causing a contemporary reference to Toxteth as a “Hamlet without a chapel”.[9] One of the lodges, Lower Lodge, is the most likely place of Horrocks’ birth and upbringing though the evidence is inconclusive[10]. The Lodge was demolished around 1862 to make way for a railway station now itself derelict, and the reputed brass plate commemorating Horrocks’ birth disappeared.

Lower Lodge Toxteth: Possible Birth Place

The Chester register of marriage licenses records the marriage on January 17th 1615 of Jeremiah’s parents James Horrocks and Mary Aspinwall. His mum’s brother (as various contemporary documents make clear) was Edward Aspinwall (1567-1632) a prominent watchmaker.[11] Edward had matriculated from Brasenose College Oxford in 1585. Though they did not own much in the immediate area, the Aspinwalls were a family of standing and property.

Jeremiah Horrocks is today comparatively unknown, but there was a flurry of interest in Victorian days, and various myths abounded. He was often viewed as both poor and sickly eg “There can be no doubt that Jeremiah came of impecunious parents and that the whole of his brief life was a struggle against poverty.”[12] Though he went up to university as a sizar or poor scholar, and obviously did not have great wealth, it seems unlikely that he suffered great pangs of poverty. Lower Lodge – described as “snug” by Victorians – was a substantial dwelling for the early seventeenth century, and not a labourer’s cottage!

Richard Mather came to teach in the new school in Toxteth in 1611, apparently living with Edward Aspinwall. Mather went up to Brasenose, Oxford, but returned at their invitation to begin preaching at the chapel (which had now been added to the school) in November 1618. He quite probably also acted as schoolmaster until his marriage in 1624 – by 1625 we know a George Whaledale was schoolmaster.[13] Richard Mather had Congregationalist ideas (i.e. saw the church as a body of covenanting believers rather than the expression of state religion in a locality). He was, however, ordained into the Anglican Church, probably in 1619. At this time (as mentioned above) the “Puritans” hoped that the state church itself would go in their direction. Mather, however, practised extempore prayer and steadfastly refused to wear a surplice, so was eventually suspended in 1633 for not keeping to the proper ceremonies. He left for America in 1635 to join other “Pilgrim Fathers” (who had sailed in 1620). The Chapel itself was never officially “consecrated” (although at one time it was recommended to be), and Congregationalists and Presbyterians continued to share it, comparatively unmolested, under a sympathetic refusal to suppress them by the Earl of Derby. The Ancient Chapel today has a brass plaque from 1856 transferred from a floor tomb to the wall, commemorating “Edward Aspinwall” – though this is a different man of this name and Jeremiah’s uncle clearly seems to have died in October 1632.

Richard Mather
Chapel Interior Now Lower Benches c1650
Toxeth Ancient Chapel Today Brass Plaque 1856

Jeremiah, then, was born into an artisan family of some standing, probably comfortably if not well off. The picture of him struggling with poverty is implausible. Instrument making was in the young lad’s family, and dexterity in making and dealing with instruments a feature of his upbringing. Tradition has it that his uncle Ted first interested the young Jerry in astronomy. He may have studied at Mather’s school up to the age of 7 years, and his family and friends’ connections were all Puritan in sympathy. An early reference to his uncle Edward Aspinwall speaks of “a learned and religious gentleman.”[14] The title “gentleman” may have been honorific – he was probably technically a “yeoman”.

Brought up in a hamlet with perhaps few children, and serious minded and studious relatives and schoolmasters, we may wonder less at the serious-mindedness of the young Jeremiah as he set out, aged only 14, for Cambridge university.

Jeremiah Horrocks (registered Horrox) entered Emmanuel College, Cambridge, as a Sizar on May 11th 1632. A Sizar or poor student might have to wait on tables or perform other chores, and probably survived on very low funds, but this route could offer a way to a degree and an appointment as a minister. The Emmanuel College was founded by Sir Walter Mildmay in 1584 on the site of a Dominican priory – and would (after Horrocks’s death) be graced with its present lovely Wren chapel. It was very much a Puritan college, and its first Master Lawrence Chadderton was a distinguished Puritan biblical scholar and preacher. In the year Horrocks entered, there graduated one John Harvard whose family later went with the New England Settlers and eventually formed Harvard University. For Jeremiah to enter at age 13-14 was not noteworthy – his friend Worthington was 14 when he entered Emmanuel in the same year. Both, in fact, “matriculated” together (i.e.. were sworn before the Vice Chancellor into the university which was distinct from the college) on July 5th 1632.

1588 Portrait of Sir Walter Mildmay Emmanuel - an Ancient Doorway
John Harvard & Emmanuel Master Lawrence Chaderton
Emmanuel "Old Chapel", there in Horrocks time, is in Puritan Style

Study at Cambridge was, of course, very different then from today. The curriculum was mostly arts, divinity and classical languages (particularly Latin). A few scraps of geometry and even classical astronomy would be included in the arts course, but nothing thorough and certainly nothing of the latest scientific works of Tycho, Galileo or Kepler. Kepler had, of course, published his three laws in 1609 and 1619, and the telescopic discoveries of Jupiter’s moons, phases of Venus, and sunspots were known. None of this was in the syllabus, but there was plenty of time spare and undergraduates could study such things if they wished. There were other European centres where astronomy was taught, but Horrocks had no means to study there. He resolved to teach himself, even though it was the difficult mathematical astronomy that interested him:

“There were many hindrances. The abstruse nature of the study, my inexperience, and want of means dispirited me. I was much pained not to have any one to whom I could look for guidance, or indeed for the sympathy of companionship in my endeavours, and I was assailed by the languor and weariness which are inseparable from any great undertaking. What then was to be done? I could not make the pursuit an easy one; and yet to complain of Philosophy [i.e. science] on account of its difficulties would be foolish and unworthy. I

Emmanuel Pond - result of  waterway there in Horrocks Day

determined therefore that the tediousness of study should be overcome by industry – my poverty (failing a better method) by patience – and that, instead of a Master, I would use Astronomical books. Armed with these weapons I would contend successfully; and having heard of others acquiring knowledge without greater help, I would blush that anyone should be able to do more than I…”[15]

What background was there in astronomy when Horrocks entered Emmanuel? Kepler had died in 1630, having predicted a transit of Venus and Mercury in 1631, and Venus not again until 1761. The 1631 Venus transit was visible in America but not in Europe and was not observed, but Pierre Gassendi observed the transit of Mercury. On this, Kepler was out by only 6 hours, and his Rudolphine Tables were generally the most accurate available. The Belgian astronomer Philip van Lansberge , however, (1561-1632),  was a follower of Copernicus and wanted to show that the ancient observations were accurate and could be incorporated into a Copernican model.[16] Lansberge’s Tabulae motuum coelestium perpetuae: ex omnium temporarum observationibus consentientes (1632) was a polemic against the “Tychonici” (Tycho, Longomontanus and Kepler), and an attempt to explain the difficulty of the precession of the equinoxes à la Copernicus.  Lansberge’s friend and co-worker Matinus Hortensius wrote a similarly anti-Tychonic account in De Mercurio in Sole Visa in 1632.  Horrocks, beginning his serious study of astronomy (still, remember, only 14-15 years old) acquired Lansberge’s works[17] after noting the praise of them in a treatise by “D H [Henry] Gellibrand, a Professor of Astronomy, in London”[18] and began to compile his own tables (Ephemerides) from the Flemish mathematician/ astronomer’s work.  Horrocks did acquire other works: in the Trinity College library in Cambridge there is his annotated copy of Philip Lansberge’s Tabulae Motuum, in which he lists twenty-four astronomical authors  he has read – of which, incidentally,  only the medieval Sacrobosco was from his own country![19] Lansberge, however, must have seemed to be the “latest and best”, and his trenchant criticism of the “Tychonists” including Kepler led Horrox to focus on Lansberge to the detriment of  the latter.  At some point (the chronology is uncertain) he testifies that, having realised the inaccuracies “I broke off the useless computation, and resolved for the future with my own eyes to observe the positions of the stars in the heavens.”[20]

In 1635 Horrocks returned to Toxteth, aged about 17. He did not graduate, although this was not all that unusual. Sometimes the expense of graduating was delayed until it might be used to gain a curacy or some preferment. We do not know what he did back in Toxteth, but he must have spent much spare time on astronomy.

Amongst Horrocks’s contemporaries at Emmanuel were not only Worthington (later Master of Jesus College) but also the mathematician John Wallis, and the Cambridge Platonist Ralph Cudworth (who influenced Newton[21] in his mechanical philosophy). Perhaps it was Worthington who, shortly before Horrocks left Cambridge, mentioned him to the young Salford cloth merchant William Crabtreee who was to be his main scientific correspondent from 1636-40. Crabtree had not been to university, but had learned Latin at school and had means to buy astronomical books so would not have been in a much different case from Horrocks. Crabtree mentions Brahe, Kepler, Galileo, Lansberge, Descartes and Gassendi – and by 1635 realised that Lansberge’s planetary tables were inaccurate. This is parallel to Horrocks and also William Gascoigne who independently made the same discovery.[22] Crabtree wrote to Horrocks, probably at Worthington’s suggestion, begging that he will excuse the liberty that he, a stranger, was thus taking, but hoping that his love for those astronomical pursuits in which Horrocks so greatly excelled would be deemed a sufficient apology. So there was formed in 1636 the circle of the Keplerri – a tiny group of those in England interested in Keplerian astronomy, but committed to astronomy as a mathematical and empirical science. Crabtree confirmed Horrocks’s suspicions that Lansberge was unreliable, and his later references (eg in The Transit of Venus) to Lansberge are very critical – in contrast to his admiration of Kepler.

We have to get out of our minds the picture that Horrocks was an “amateur” astronomer, for such categories applied anachronistically can only be misleading. Cambridge had no department and no professor, there were no official observatories in England, there was no obvious scientific society or group, and certainly nothing like a degree/career structure in astronomy. Lack of funds and lack of any rich patron were obvious problems, but that Horrocks had no recognised “post” or qualification was almost inevitable.

Near the end of 1637 he commenced a treatise: Jeremiae Horroccii Anti-Lansbergianus, sive disputationes in astronomiam P. Lansbergii, quibus perspicue demonstratur, hypotheses suas nec caelo nec sibi consentire, later retitling and rewriting it as Astronomiae Lansbergianae censura et cum Kepleriania comparatio. One does not even need to be able to read Latin to get the gist – Lansberge NO! Kepler YES! Various other treatises were compiled in this time. Horrocks was writing not only on planets, but on the moon on which his work was original and important. He published nothing, however, lacking both the means and probably a circle of potential buyers to do so. The Keplerri were a tiny group in England, and not personally in contact with Continental scholars.

That he was compiling tracts in Latin, the common scholarly language of Europe, seems to indicate an intention at least to publish. These were not purely personal notes, but were intended to enter upon the world at some stage. What plan he may have had in mind we cannot now tell.

In this period Horrocks was working on his lunar theory – eventually showing that the moon’s orbit was elliptical.  Horrocks also had an interest in comets, concluding that they “move in an elliptical figure or near to it.” He commenced a series of observations on the tides, working on this for three months. He wrote to Crabtee about this, but no papers survive relating to his observations or theories.

St Michael's Church: Hoole

The Church today is an active Parish Church with well attended Sunday morning services and a Rector, Rev Harry Pugh, who appreciates its Horrocks connection (it is sometimes opened to visitors on Wednesday afternoons in summer).

The font and two 1631 pews are still in the church, but additions were made:

Sunday Serivce
1696: The present pulpit
1719 West tower and gallery
1858 Chancel (Horrocks chapel)
1859 Tower clock
1859 Memorial tablet
1874 Memorial windows
1994 Digital computer organ
1997 Floodlighting
St. Michael's Church
Rev Harry Pugh

Rev Harry Pugh in St Michaels - 2001. The Horrocks Memorial Tablet is on the left wall and just beyond it the window portraying a telescope. The window portraying Horrocks is at the far end.

On 1st June 1639 Horrocks wrote to Crabtree: “Next week I remove to Hoole, a village about 5 miles from Preston.”  Much Hoole was a small,   damp country village, set between “the Moss” to the East and North, the wetlands of the coast and down to Martin Mere on the West and South. We have no certainty about what he did in Hoole, but the strong tradition is that he was tutor to the children at Carr House. The latter was built in 1613 (as noted in an inscription on the stone porch lintel) by Thomas Stones of London Habersdasher and Andrewe Stones the Amsterdam merchant, for their brother John who was a farmer and landowner. Thomas also built (of similar, probably Dutch, bricks) a chapel of ease (St Michael’s) in 1628 – a date carved on its wooden lintel. An octagonal font was given by John Stones in 1633, and when the chapel became a parish church in 1641 Stones was given its patronage. The curate there during this time was probably[23] Robert Fogg, who was given the new living in 1641.

Was Horrocks a curate at Hoole?   He is so named on the plaque now in St Michael’s Hoole (erected in 1859 by the nineteenth century Hoole Rector Robert Brickel), and on the (1874) plaque in Westminster Abbey. In the Memoir attached by Rev A B Whatton to his 1859 translation of Venus in Sole Visa, he accepts that to become ordained “young men are now required to be twenty-three years of age”. Whatton notes, however, a mention of Reverend Mr Horrox in a treatise by John Gadbury (which he does not date), also one by the early eighteenth century astronomer Costard, and by Hearne in the 1720’s. He suggests that in the 1630’s the Bishop could simply exercise discretion without any special dispensation, and ascribes the work to “Rev. Jeremiah Horrox”. Is there other evidence?  In his work Venus in Sole Visa Horrocks states:

“I watched carefully on the 24th from sunrise to nine o’clock, and from a little before ten until noon, and at one in the afternoon, being called away in the intervals by business of the highest importance which, for these ornamental pursuits, I could not with propriety neglect.”

What were these duties to which Horrocks refers? The Victorians thought they were duties of a curate. Actually, if the duties really were those of a curate their apparent brevity would be very surprising. More probably they were to do with being tutor at the house, or perhaps his “business” as any serious Christian would be to attend the church. Most crucially, none of Horrocks’s friends or contemporaries mention any ordination or refer to him either as “Rev Mr Horrox” or “Rev Jeremiah Horrox”. Crabtree, for example, sadly wrote the memorandum: “Letters of Mr. Jeremiah Horrox to me of the years 1638, 1639, 1640, until his death on the morning of 3rd January…” No title of “Rev.” is given as it surely would have been. It seems virtually certain that Horrocks’s supposed ordination/curacy was a myth.[24] He was probably called upon to pray, catechise or say grace for the Stone family, and may even have been some kind of lay reader, though we cannot be certain.

Carr House, where Horrocks was probably a tutor, still stands, and now has a plaque up outside to mark the local view that Horrocks observed the transit of Venus on 24th November 1839 (put up by Chorley Civic Society – an event in which the University of Central Lancashire was involved in the late ’90s). Kepler had calculated a transit in 1631, but Horrocks realised that in fact the transit occurs twice with an eight year gap – so would occur in 1639 but then not again until 1761/69 and then 1874/82 etc. Miss it (next one is 2004/12) and there’s a long wait!  Horrocks realised it was coming only weeks before the event – an amazing “coincidence” unless you have a Puritan view of providence.

The house is a listed building and retains a beauty that is not well conveyed in a black and white picture. The most probable room for his observation (assuming it was made here) is in the window on the first floor above the porch. This is, in fact, the only window from which the sun would have been observable during the whole of the relevant day 24th November. Horrocks had also written to his younger brother and to Crabtree in Manchester advising them to observe on this day. Crabtree did so and Horrocks says that: “Rapt in contemplation he stood for some time, scarcely trusting his own senses, through excess of joy.”  Crabtree, however, was not able to make any actual measurements – it was cloudy in Manchester as so often!  No one else in Europe seems to have known about the event and observed it.

Details of the observation will be given under his works below. At this point it is useful just to say that he observed on the day before he had calculated the transit would come, and seen nothing. He then says:

“I watched carefully on the 24th from sunrise to nine o’clock, and from a little before ten until noon, and at one in the afternoon, being called away in the intervals by business of the highest importance which, for these ornamental pursuits, I could not with propriety neglect. But during all this time I saw nothing in the sun except a small and common spot… This evidently had nothing to do with Venus. About fifteen minutes past three in the afternoon, when I was again at liberty to continue my labours, the clouds, as if by divine interposition, were entirely dispersed, and I was once more invited to the grateful task of repeating my observations. I then beheld a most agreeable spectacle, the object of my sanguine wishes, a spot of unusual magnitude and of a perfectly circular shape, which had already fully centred upon the sun’s disc on the left, so that the limbs of the Sun and Venus precisely coincided, forming an angle of contact. Not doubting that this was really the shadow of the planet, I immediately applied myself sedulously to observe it.”[25]

Horrocks had about thirty-five minutes to observe the transit before apparent sunset at 3.50 pm, making three careful measurements at 3.15, 3.35 and 3.45. Hoole residents may not be altogether flattered by Horrocks’s comment at this point that the observation was made in “an obscure village… about fifteen miles to the north of Liverpool.”  Liverpool itself, of course, in those days, was not a centre of industry, but a place (as Whatton remarks) of “comparative insignificance”.

Horrocks’s letters from Hoole cover 8th June 1639 to 12th April 1640 after which he returned (by summer 1640) to his family in Toxteth. We do not know what his employment was, but he continued to write to his friend Crabtree concerning astronomical matters. He died very suddenly on 3rd January 1641, we do not know what from. Crabtree lamented this sudden loss, on the very day before Horrocks had planned a trip to see him. Horrocks is believed to have been buried in an unmarked grave in (possibly actually inside the building) the old Toxteth chapel, which is pictured above (p. 7.4). Both Crabtree and Gascoigne died shortly afterwards in 1644 – we do not know how Crabtree died but Gascoigne died in the Royalist cause, probably at Marston Moor.

Horrocks’s Christian Beliefs

Allan Chapman well says:

“…as an English Protestant, Jeremiah Horrocks would have found far fewer restrictions to scientific research than a continental Catholic would have felt after 1633. Quite simply, the Church of England had no policies on science whatsoever, and during the 1630s, the English bishops were more concerned with the theology of the Divine Right of Kings than they were with the shape of the orbit of the Moon.

What shines through Jeremiah's writings is a sense of awe and praise for the Deity who could make a universe that was so intricate and so beautiful. One also perceives his sense of privilege at being the first human creature to learn of certain things - such as the shape of the Moon's orbit - or to see the transit of Venus.”[26]

However Chapman also says:

“We can suggest, however, that if Jeremiah was in any way employed by the Stones family during his stay in Much Hoole, he was not a Puritan. For the Stones family had presented a font to the parish church of St. Michael, along with a communion chalice and platten. These were sacramental vessels, and as such, strongly disapproved of by many Puritans, who regarded the sacraments as 'Popish'. The Stones family also endowed Much Hoole as a new parish in the Anglican Communion in 1641, with Robert Fogg as the first rector. It is unlikely that a family that displayed such marks of loyalty to the sacramental offices of the Anglican Church would have employed a theological radical.”

This seems a very dubious argument. Puritans were Calvinist/Reformed in theology, and not part of the Radical Reformation or Anabaptist movement. They objected to Laud’s reintroduction of crosses, crucifixes and surplices, and they wanted to use extempore rather than liturgical prayers. But they made no suggestion that a Church should not have a font or vessels to administer sacraments – how else could these be given?  The suggestion that Puritans regarded sacraments as “Popish” is surely mistaken. That Horrocks’s family associated with the Puritan Richard Mather and Horrocks went to the Puritan college Emmanuel would not necessarily indicate his own views. But Horrocks makes the following comment on Kepler – whom he calls “the most learned astronomer who ever lived”:

“Kepler’s astronomy differs from mine as his religion: he gives the planets a divers nature (good and bad) that they may either come to the Sun, or fly away at their pleasure, or at least (as his second thoughts are) so dispose themselves (in spite of the Sun's magnetical power) that the Sun is bound to attract or repel them according to that position, which themselves defend against all the Sun's labouring to incline their fibres. I, on the contrary, make the planet naturally to be averse from the Sun and desirous to rest in his own place, caused by a material dullness naturally opposite to motion and averse to the Sun without either power or the will to move to the Sun of itself. But then, the Sun by its own rays attracts and by its circumferential revolution carries about the unwilling planet, conquering that natural self-rest that is in it; yet not so far, but that the planet doth much abate and weaken this force of the Sun, as is largely disputed afore… So just do the papists, whose free will to do good or bad, can by its own strength go to God or fly from Him, or at least frame their own actions, as that God is bound to save them or damn them, volens, nolens. But I will confess myself not equally composed of good and bad, that myself may give either to flesh or spirit the upper hand; but rather wholly desirous to rest in myself, and wholly averse from God, and therefore justly deserve (as the fixed stars from the Sun) to be blown away from God in infinitum; but that God, by his Son's taking on Him man's nature and the undeserved inspiration of His spirit, doth quicken this dullness, nay, deadness, of my nature, yet still, ah me! how doth it choke and weaken their operation.”[27]

Kepler, indeed, thought that the orbits were affected by the planets’ own magnetic forces – Horrocks’s slightly different theory places all the determinative action in the sun itself. But on the theology we remember that Kepler – otherwise a fairly orthodox Phillipist Lutheran – rejected the Reformed view of predestination and advocated freewill. Horrocks

clearly here rejects the ideas of freewill taken by Kepler but also eg by Erasmus and most of the Radical Reformation. He is advocating classic Reformed Puritanism – every part of the conversion/salvation process in individuals is divinely controlled and ordained. Horrocks was, in short, a Puritan – this much was not part of any later Victorian myth. How extreme he may have been in this view is not apparent from his comments. The Stones, family, however, can hardly have been surprised that a man who came from Emmanuel college held such views – and there is no reason to suppose that they would have objected to them. The font presented by John Stones is a perfectly plain and serviceable one, with neither ornate decoration nor even a cross on it.

St Michaels' Font

Having, however, made some criticism of Chapman (to whose work this present account is so much indebted) it seems appropriate to quote appreciatively his further comment in the same work on the more general science-religion issues of Horrocks’s times:

“Horrocks’s attitude towards science - as the great revealer of God's design to the human intellect - was shared by the following generations of English scientists who came to form the Royal Society in 1660, and published his surviving letters and treatises in 1672. John Wallis, who edited Horrocks's Opera Posthuma, was a clerical mathematician who refused a Deanery to remain a professor. The Royal Society's effective founder, the Oxford astronomer John Wilkins, became Bishop of Chester in 1668, and would have come thereby to have spiritual supervision over Much Hoole which was then in the diocese of Chester. Seth Ward moved from an astronomical professorship at Oxford to the Bishopric of Sarum at Salisbury, while the man who wrote the first history of the Royal Society and its work in 1667, Thomas Sprat, became Bishop of Rochester. The ‘father of English Chemistry’, the Hon. Robert Boyle, was invited by King Charles II to take Holy Orders so that he could receive preferment in the Restoration Church, but refused, arguing that he felt more able to promote the Christian faith if he were not obliged to do so by law. These men represented the intellectual cream of Horrocks’s generation, and show how powerfully they unified the investigations of science not only with their Christian faith, but also with the holding of ecclesiastical office. Had Jeremiah lived into his fifties rather than dying at 22, he could well have been one of their number.”

Horrocks’s Work and Reputation

After the death of the three friends, some of the relevant Horrocks papers disappeared with his brother Jonas.  Some passed into the hands of  Lancashire historian Christopher Townley where they were consulted appreciatively by Jeremy Shakerley, who wrote three books on astronomy in the mid seventeenth century.[28] Some of the Horrocks papers passed into the care of John Worthington who had been at Emmanuel with Horrocks.[29]

"Venus in Solae Visa"

Huygens saw a copy of “Venus in Sole Visa” and the work was published (still, of course, in Latin) in 1661 by his friend the self-financed Dantzig astronomer Johannes Hevelius (1611-1697). He added his own explanations to the work (though in fact Flamsteed thought that these were of dubious value), and appended it to his own parallel work on Mercury.

In the year 1666 the Royal Society became interested in the Horrocks papers, commissioning Dr John Wallis (who entered Emmanuel with Horrocks) to collect and edit what he could. After many difficulties (some papers lost in the great fire and the Royal Society generally cash strapped!) he published in 1672 Jeremaie Horrocci Liverpoliensis Angli ex Palinate Lancastiae Opera Posthuma – letters and papers of Horrox in Latin.

Chapman also suggests:

“Sir John Moor, the motivating force behind the founding of the Royal Observatory, may have known Horrocks as a young man in Lancashire, and was certainly a friend of Christopher Townley, who preserved the Horrocks papers after Crabtree’s death in 1644… Flamsteed, whose appointment as Astronomer Royal in 1675 owed much to Moor, had seen and transcribed some of Horrocks’s correspondence at Towneley Hall in the 1670’s.”[30]

Horrocks’s work may well have highlighted the paucity of observation facilities in England compared with those eg in Italy or Germany. Flamsteed, although Astronomer Royal at the new Royal Observatory, was receiving insufficient funds from the government (so what else hasn’t changed!), and having to supplement his funds with a church living. Perhaps this helped him sympathise with Horrocks with his financial limitations! Certainly he valued highly Horrocks’s work. Newton’s first edition of the Principia (1687) said:

“I am not quite certain about the diameter of the earth as seen from the sun. I have assumed it to be 40”, because the observations of Kepler, Riccioli and Vandelini do not allow of its being much greater. The observations of Horrox and Flamsteed make it somewhat less.”

Newton continued to write of the ideas of Flamsteed-Horrox. In fact, Flamsteed took what Westfall describes as a “fatherly pride” in Horrocks lunar theory, writing (perhaps not with great tact) to Newton on 3rd Nov 1694:

“when you have determined what corrections or additions are to be made to that theory which it was my Good fortune to meet with & usher into ye light, I doubt not but you will import them to me as freely as I did the observations Whereby you limit or confirme them to you.”[31]

The second (1713) edition of the Principia left all this out. Newton, however, continued to value Horrocks, noting in this edition that Horrocks was the first to show the moon as moving in an ellipse with the Earth at one focus. In his separate work The System of the World he says Horrocks’s lunar system as  “the hypothesis of Horrox which is the most ingenious, and, if I do not deceive myself, the most accurate of all.” 

Horrocks was a natural link between Kepler and Newton, but we should not overestimate his influence. Exaggerated 19th century claims (eg in Whatton’s and Brinkley’s Memoirs in 1859) that Newton derived his idea of gravity and/or inertia from him are mistaken. Horrocks speaks still of “impetus”, and Kepler’s ideas on gravity are probably closer to Newton’s.

Horrocks Memorials

From the point of view of the history of science it is interesting to follow the waxing and waning of interest in Horrocks – especially in his home country. In the nineteenth century there was a surge of interest in and memorials to Horrocks in England.

St Michael’s Church Toxteth -Park

A new Parish Church of St Michael (with iron pillars) was built in Toxteth near to the ancient chapel (now Unitarian), and in 1826 a white marble scroll on a black slab commemorating “Jeremiah Horrox” as “one of the greatest astronomers this Kingdom has produced” was mounted prominently at the front of the church.

White marble scroll St Michael's Church

Whatton’s Memoir

In 1859 Whatton’s translation of “Venus in Transit” was published- this was the first English version. With it was published Whatton’s Memoir, showing Horrocks as poor and also as almost certainly ordained – in spite of acknowledging that he was officially too young.

The word of our God shall stand forever 1963 religion and science in fellowship 1874

The picture is pure Victorian imagination as it shows the sun projected on a sheet, whereas Horrocks actually used a piece of paper with degrees drawn on it. We do not know what he really looked like.


Born at Liverpool, Educated at Cambridge,
Curate of Hoole,

"The Wisdom of God in Creation was his study from early youth

For his wonderful genius and scientific knowledge,
Men speak of him as-
"One of England's most gifted sons."
"the pride and boast of British Astronomy."

Amongst his discoveries are
The nearest approximation to the Sun's Parallax,
The correct Theory of the Moon,
And The Transit of Venus.

But the Love of God in Redemption was to him a yet nobler theme.
The preaching of Christ Crucified a yet higher duty;
Loving Science much he loved Religion more;
And turning from the wonders of Creation to the glories of the Cross He expressed the rule of his life in these memorable words:

In memory of one so young and yet so learned,
so learned and yet so pious,
This Church in which he officiated has been
Enlarged and Beautified. 1859.

Westminster Abbey

In 1874, after much lobbying, a memorial was mounted in Westminster Abbey opposite that to Newton.  It reads:

In memory of Jeremiah Horrocks, Curate of Hoole in Lancashire who died on 3rd of Jan, 1641 in or near his 22nd year.

Having in so short a life detected the long inequality in the mean motion of Jupiter and Saturn discovered the orbit of the moon to be an ellipse determined the motion of the lunar apse suggested the physical cause of its revolutionand of Venus which was seen by himself and his friend William Crabtree on Sunday the 24th of November (O.S.) 1639.[32] This tablet facing the monument of Newton was raised after the lapse of more than two centuries. Dec. 9, 1874.

The Eyre Painting

Westminster Abby

Presently on loan from the Walker Gallery and hanging in the Liverpool Museum Planetarium is a famous painting by Eyre Crowe BA. The painter said that he modelled the room on that in Carr House, which he claimed in 1891 to have visited, though the Puritan outfit seems unlikely and elaborate equatorial telescopic apparatus unhistorical. The painting is now very dark, and is unclear without computer enhancement.

The Eyre Painting

The Ancient Chapel Memorial - Toxteth

In 1891 a tablet was put up in the (now Unitarian) Ancient Chapel of Toxteth (pictured p. 6.4). Horrocks is still Horrox, but has been defrocked again. The tablet finishes:

“It is believed that before going to Cambridge he was a pupil of Revd Richard Mather the first minister of this chapel, and that within its precincts he was buried.”


Nineteenth century and early twentieth century English academics tended to make much of Horrocks. This seems, however, to have faded during the twentieth century. Michael Hoskin, sometime Head of Department of History and Philosophy of Science in Horrocks’s Alma Mater, leaves him out of his compendious Cambridge Illustrated History of Astronomy (1997). Kitty Ferguson, in her popular book on Measuring the Universe (1999) mentions Harriot and Gascoigne but leaves out the Englishman who first measured accurately our nearest planetary neighbour, and pushed up the key measurement of solar distance to nearly 60 million miles.

Horrocks’s Work

Some Technical Background

Some comment has already been given on technical background, but we need here to expand this (which may involve some slight repetition). To determine the distance and amount of solar parallax. Ptolemy [33] had worked as follows:

Illustrations of Ptolemy's Reasoning
  1. The earth’s radius was known.

  2. The moon’s distance was found by parallax (ie observing at different points on the earths surface against fixed stars assumed very distant) and at apogee (ie furthest away)  is 64.17 earth radii (= 209 thousand miles).

  3. The moon’s apparent diameter is equal to the sun’s in total eclipse at apogee distance – with figures 31′ 20″ (the modern lunar figures are 29′ 22″ at apogee and 33′ 31″ at perigee giving mean 31′ 5″, the mean for the sun is 32′)

  4. The width of the Earth’s shadow cone as the moon passes through it is little less than 2.6 times the moon’s width.

This produced a solar distance of 1210 earth radii (about 3.9 million miles). Ptolemy also estimated that Venus was about one tenth of the sun’s angular diameter. The Arab/mediaeval distances differed little, and Copernicus (as we have seen) adopted similar dimensions. Galileo insisted in his Dialogue that these apparent diameters and distances were wrong, but did not say what they should be.

Kepler gradually lost faith in the traditional Ptolemaic method for estimating the parallaxes and distances. He had, however, no obvious alternative, and resorted to considerations of harmony. By the introduction to his Ephemerides in 1617[34] he arrived as a solar parallax of 2’ and a distance of about 1800 e.r. ie 7.1 million miles. By 1618 Kepler had fairly accurate relative distances of orbits for the planets – relating, of course, to his planetary laws and in particular the third law discovered that year. Actual distances, however, were elusive. By now the only method for measuring parallax/distance he thought useful was consideration of the time between lunar dichotomy (when the moon appears as exactly a half) and quadrature (when it forms an angle of 90o in relation to the sun). Kepler hoped that the telescope would now enable these times to be measured more precisely – though he was disappointed when he tried it. Kepler’s system is a mixture of the empirical and ideas of the harmony (in mathematical terms) which must exist.[35] It is important to remember (and this was explored in the notes on Kepler), that one cannot separate Kepler’s mathematical astronomy from his supposed “number mysticism”. Kepler began from a belief that the world was made by a rational God, committed to mathematical harmony, and that therefore would finally be decipherable in terms of beautiful mathematics. His third law was no more inherently rational or less “mystical” than his theory of orbits based on the five perfect solids. Horrocks’s approach was virtually identical in all respects. Details were changed, and the same approach led to slightly different conclusions, but he too was looking for mathematical harmony. In some ways, as was argued in the Kepler notes, mathematical astrophysicists may be looking for analogous “beautiful” mathematically based systems today – with or without reference to any God.

In any event, by 1618 Kepler had concluded that solar parallax was nearer 1′ than 2′, and this gave a solar distance of 3469 earth radii which (using a mean earth radius of 3960 miles) gives about 13.7 million miles (the modern figure is, of course 93.0 million). The lunar distance Kepler found to be 59 earth radii giving 1.98 thousand miles (the modern figure for the mean lunar distance is 2.40 thousand miles). Kepler held that the volumes of the planets were proportional to their mean distances from the sun, their densities proportional to the inverse root of their mean distances, and the solar “push” (anima motrix) to make them orbit was therefore equal. If planetary densities were equal then this would lead to their orbital periods being proportional to their distances. Kepler’s third law gave a different result, and so he deduced that this was because of their varying densities.

Transits of Mercury are more common than of Venus – about a dozen occur each century. Kepler had greatly overestimated the apparent planetary diameters, with Venus expected as about a quarter of the sun and Mercury similarly scaled - he therefore thought that a camera obscura would reveal the transit. In the event only three astronomers (Remus, Cysat and Gassendi) observed this November 1631 Mercury transit, all by projecting with a telescope. Pierre Gassendi (or, as Horrocks calls him, “illustrious Gassendi”![36]) made the best observations, and was astonished at how small the planet was. He made the apparent diameter only 20″ instead of the 15′ he had expected. Gassendi, in fact, observing through intermittent clouds, almost

Modern View of Sizes
missed it altogether until he realised that the motion of this tiny dot across the solar disc meant that it could only be Mercury. Remus made it 18″, which fitted well his own schema that supposed that apparent diameters when seen from the sun were the same.  

Philip van Lansberge, as noted, was Copernican rather than Keplerian,  reverted to the Hipparchic-Ptolemaic approach on measuring distances, and was critical of Kepler’s results. His colleague and follower Hortensius, however, defended Gassendi’s view of the smallness of Mercury against various critics who claimed that it was some kind of optical illusion.

When Horrocks entered Emmanuel, then, in 1632, there were exciting new theories and observations, but also many open questions. Kepler had been dead less than two years, Galileo’s Dialogue was about to create a stir in Italy (although about 24 years out of date since it ignored even Kepler’s first two laws let alone the third), and the amazing telescopic discoveries of the previous two decades had been crowned by Gassendi’s bombshell that Mercury was tiny. We need to note that in terms of planetary prediction (and therefore predictions of transits) very small errors could make a big difference. It was, in fact, wrong assumption about solar parallax and refraction that had led to Kepler (and his assistant Jacob Bartsch) missing the fact that a second Venus transit would occur in 1639. Astronomers were struggling to find new ways to improve accuracy.

Horrocks’s Work on the Moon

Lunar theory is, of course, inherently complex, for the moon reacts not merely to the Earth’s gravity but also to that of the Sun, and the Earth-moon system itself reacts complexly in orbiting the Sun.  This should be borne in mind.

In his early letters to Crabtree in Autumn 1636, Horrocks (still only 18 years old) indicated that he had found Lansberge’s lunar theory faulty, and inaccurate in predicting the durations of lunar eclipses (which were, of course relevant to Lansberge’s method for solar parallax as above).[37] On 14th January 1637 Horrocks informed Crabtre that he now had his own lunar theory. Only in May that year did he get a copy of Kepler’s Rudolphine Tables. He wrote:

“I judge it to be a most perfect work… Embracing his hypothesis as true, I have undertaken to correct his tables.”[38]

Wilson explains[39] how Horrocks tried various ways of adapting Kepler’s lunar theory. He suggests that Horrocks was using the duration of lunar eclipses to measure eccentricity:

“From the apparent angular semi-diameter of the Sun, and the horizontal parallax of the Earth, he can calculate a value for the semi-angle of the cone of the Earth’s shadow; the calculation is relatively insensitive to the value of the horizontal parallax, and since Horrocks has reduced this to a lower and thus more correct value than any of his predecessors, namely 25″, his value for the semi-angle of the cone is almost exactly right.”

The duration of a lunar eclipse obviously depends on both the moon’s speed and its distance from the earth (the shadow being less when hearer), and in doing careful measurement and calculation Horrocks found (effectively) that when the moon is in between the Earth and the Sun (ie in syzygy) its ellipse is elongated (ie eccentricity increases). In Horrocks’s final lunar theory, then, both the eccentricity of the lunar orbit, and the apogee (its furthest point from the earth) oscillate. This, in effect, was similar to an earlier model of Kepler’s, which the latter had abandoned.

Wilson suggests that the reason for the divergences between Kepler and Horrocks lay in the issue on which Horrocks was quoted above on page 7-13. Kepler had suggested that magnetic fibres within the planets themselves might cause alternate attraction and repulsion, which, operating with the basic motive force of the Sun, would cause the elliptical orbits. In his Philosphicall Exercises Horrocks explains that this seems irrational for:

“…if the Sun be able to carry about the whole body of ye planet, questionless it will be much more able to turn ye friendly part to itself and so unite it to itselfe.”[40]

Horrocks, in contrast, finds in the conical pendulum a partial model for elliptical orbits. The pendulum bob moves in an oval and the apsides of this oval advances just as with planetary ellipses. It is worth quoting here from Wilson’s conclusions to his study:

“Horrocks assumes that, just as the pendulum bob is attracted to the centre of its oval, so is the planet attracted to the Sun; and contrary to Kepler's conception, it is never repelled. Both pendulum bob and planet must receive a transradial impulse if they are to move in rounded orbits instead of directly toward the centre of attraction, and in the planet's case Horrocks locates the source of this impulse in the rotation of the Sun. A certain imbalance between the transradial and central forces is responsible for the forward motion of the apsides.

The only discrepancy is that the conical pendulum produces a concentric oval, while the planetary oval is eccentric. A wind, Horrocks suggests, could cause the oval orbit of the conical pendulum to become eccentric; in the case of the planets, the displacement must be due to an internal propensity. The internal propensity, Horrocks conjectures, is a tendency for the planets to rest in the place where they were first placed, namely, their aphelia. He devotes considerable effort to the attempt to locate the moment of the creation of the planets, on the fourth day of some past week, in which all the planets would be at their aphelia.

If the explanation seems unbelievable to post-Newtonians, we should yet recognize that it is an important step beyond Kepler. It relies, not on a complicated internal structure of the planet and Sun, but on the Sun's attraction and on properties of matter thought of as inertial.…

Thus, where Kepler had explained the planetary motions by special mechanical contrivances, designed by a providential artificer and arranger, Horrocks now saw them as the result of the Sun's force combined with the inertial properties of matter… He could not, of course, account for the oscillations…

But then, even the explanation of the evection that Newton offers in the Principia is less than satisfactory, since in accounting for the oscillations of eccentricity and apse he uses only the radial component of the Sun's perturbing force, and leaves the transradial component out of account. And without Horrocks's lunar theory as a starting-point, he would have had available neither a correct statement of the facts of the Moon's second inequality, nor one inviting any manner of Newtonian explanation.”[41]

Horrocks was hailed in some nineteenth century eulogies as having almost invented Newtonian gravity and inertia.[42] This is exaggerated, and some of the things cited are actually already in Kepler’s work. However there are aspects in which Horrocks does form a kind of bridge between Kepler and Newton. All three men, of course, were absolutely convinced that the cosmos was the work of a great and mathematical designer, all three looked for a mathematical harmony in physical nature, all three were great mathematical and empirical astronomers.

Horrocks’s Solar and Planetary Work

Improved solar theory was essential for improved planetary theory and especially planetary prediction. Horrocks therefore worked on solar parallax, rejecting the old Ptolemaic method (still used by Lansberge) as too full of inherent errors to be of use. Horrocks’s reasoning was that parallax for Venus is undetectable, yet must (when Venus is near to inferior conjunction) be four times that of the sun.[43] Horrocks’s figure of 14-15″ was much smaller than Kepler’s, and Horrocks came to believe that many of Kepler’s errors were due to his inflated figure of solar parallax.. Horrocks also calculated an eccentricity of around 0.01735 – the modern figure is 0.0167[44]. Horrocks’s figure for equation of centre (relating to the angle of the major elliptical axis) was out by only +3′ – he had arrived at a more accurate solar theory than anyone else so far.

Wilson points out that improvements in solar theory led to improvements in planetary theory.[45] In a letter to Crabtree of 19th January 1638 Horrocks suggests increasing Kepler’s figure for eccentricity of Mars of 0.09265 to 0.09292 (the present value put on it is 0.09303). This made Horrocks’s predictions (and he made many of his own observations to check them) accurate to within 1-2′ of arc.

For Venus, parallel improvements were of great significance, as they led to his recognition (in Autumn 1639) that transits of Venus occurred twice in each of the major cycles Kepler had found, with a gap of eight years between the pairs of occurrences. Horrocks wrote to Crabtree on 5th November 1639:

“The reason why I am writing you now is to inform you of the extraordinary conjunction of the Sun and Venus which will occur on November 24. At which time Venus will pass across the Sun. Which, indeed, has never happened for many years in the past nor will happen again in this century. I beseech you, therefore, with all my strength, to attend to it diligently with a telescope and to make whatever observation you can, especially about the diameter of Venus, which, indeed, is 7' according to Kepler, 11' according to Lansberge, and scarcely more than 1' according to my proportion.”

The telescopic projection method was essential because a camera obscura (as Kepler had suggested) would not work with a Venus as small as Horrocks expected.

To observe the transit Horrocks says he: “described on a sheet of paper a circle whose diameter was nearly equal to six inches, the narrowness of the apartment not permitting me conveniently to use a larger size.”[46] Onto this he projected the image of the Sun using a telescope. The kind of telescope he used was probably Galilean rather than Keplerian in design. During the transit he took three measurements at 3.15, 3.35 and 3.45 pm. He found that Venus’s diameter was about 1/25th of that of the Sun. Horrocks found the longitude and latitude of Venus from the centre of the Sun, and demonstrated that his estimate was robust ie not altered much if there were observational error.

Venus in Transit

Horrocks calculated Venus’s apparent diameter during the transit as 76″ and accepted Gassendi’s 20″ for Mercury. Critics had claimed regarding Gassendi’s observation of Mercury that it appeared over small because of the Sun’s rays shining around it. Horrocks also tried other means to check the smallness of planetary diameters. On 7th and 29th January 1640 he used a pinhole and moved an iron needle back and forth until it just covered the planet to observe the exact size of Venus (and other planets). The diameter of the needle was measured by winding a thread around it numerous times. In arguing for a small diameter Horrocks utilised general arguments in Galileo’s Dialogue, but apparently had not see his Letters on Sunspots which gave estimates generally confirming Horrocks’s figure.

From Gassendi’s and Horrocks’s measurements, Mercury and Venus would have apparent diameters of about 28″ as seen from the sun. Horrocks extended this mathematical harmony to other planets – though it has to be said that the measurements made of them were by methods far less reliable. He then asserts as a “probable conjecture”[47] that the Earth may also appear as 28″ from the Sun. So he challenges his fellow Copernicans (“for I esteem not the opinions of others”):

“…what prevents your fixing of the Earth as the same measurement, the parallax of the Sun being nearly 0′14″ at a distance, in round numbers, of 15000 of the Earth’s diameters?”

This figure would make the Sun 59.4 million miles away – larger than anyone had previously suggested.[48]

Horrocks rejected Kepler’s speculations which related planetary distances to planetary volumes. For one thing, the discoveries of Gassendi on the size of Mercury and Horrocks himself on the size of Venus would not fit this. Horrocks made a suggestion (which he did not know had already been made by Remus) that is that their distances were proportional to their diameters. He had suggested this in 1639 to Crabtree before the transit, and now felt that it was confirmed. Horrocks was, however, well aware that his measurements were speculative, asserting:

“I demonstrate in round numbers a very great distance, outstripping all senses. I shall, therefore, not consider someone to dissent from me if he adds to or subtracts from the distance of the Sun even a thousand semi-diameters of the earth. And the same is to be said much more of the size, with which, if you were to double it, you would not find me disagreeing very much. For a small and imperceptible change in the Sun’s parallax would produce all this and more…”[49]

Horrocks was, to some extent, “lucky” in the particular set of assumptions he made, assumptions that made him come closer to certain figures (eg the distance of the Sun) than anyone had done previously. The “luck”, however, went along with some careful observational and mathematical work. Horrocks was very much in the Keplerian tradition – he recognised the difference between speculation and reliable measurement even though he mixed the two in an attempt to find a system that reflected the mathematical harmony of a universe made by a loving and rational Creator.

Post Horrocks

Horrocks’s lunar theory was, as we have noted, taken up by Newton, who never arrived at a theory he found satisfying on it. On more general issues of the measurements made of planetary and solar parallaxes Van Helden traces some of these in the years after Horrocks’s death. By 1650 the old sizes were discredited, but no agreed method was available to get better figures. Convex eye pieces had by now replaced concave, and various micrometers were being tried Christiaan Huygens (1629-1695) made various estimates which gave rise to a solar distance slightly higher than the modern estimate – though some of his assumptions were arbitrary:


Thomas Streete (1622-89), in his 1661 Astrononomia Carolina[50], used Huygens’s micrometer measurements but Horrocks’s parallax figure. He also seems to have followed Horrocks in asserting the exactitude of Kepler’s third law. By the time of Flamsteed in the 1670’s figures fairly close to modern ones were arrived at, though they remained uncertain. Halley tried using the transit of Mercury in an expedition in 1676-78 to determine parallax, but remained dissatisfied. Ironically (in view of Horrocks’s work) he concluded that the only reliable method would be to observe the transit of Venus – but he was unable to await the next one in 1761! Others did, however, make careful measurements in 1761[51] and 1769, getting the first accurate measurements for parallaxes of Venus and the Sun. Finally, Venus in Sole Visa established the size of our solar system, as Horrocks had believed it would.


The primary sources for Horrocks are:

Jererniae Horrocci Liverpoliensis Angli ex Palinatu Lancastriae Opera Posthuma, edited by John Wallis (London 1673).

A copy of this is in Liverpool Central Reference Library, and another in the Bodleian Library – but be warned that it is all in Latin even if the diagrams are pretty!

Memoir of the Life and Labours of Jeremiah Horrocks, To Which Is Appended A Translation of His Celebrated Discourse The Transit of Venus across the Sun, by Arundell Blount Whatton B.A. LL.B. (London 1859).

This classic translation of the Discourse is being placed on our website.

Secondary Sources:

A Chapter of Romance in Science 1639-1874: In Memoriam Horroccii. [Brickel’s work on Horrocks, to commemorate the Building of the Brickel Vestry 1998 – available from St Michael’s Church Hoole].

J. E. Bailey, “Jeremiah Horrocks and William Crabtree, Observers of the Transit of Venus, 24. November 1639”, The Palatine Note-Book II (Manchester 1882), pp. 253-66.

J. E. Bailey, “The Writings of Jeremiah Horrox and William Crabtree”, The Palatine Note-Book III (Manchester 1883), pp. 17-22.

W. F. Bushell, “Jeremiah Horrocks; the Keats of English Astronomy”, Mathematical Gazette 43, 343 (February 1959), 1-16; reprinted in the North-West Astronomers Series by the Liverpool Astronomical Society, 1992.

Allan Chapman Three North Country Astronomers (1982).

Allan Chapman, “Jeremiah Horrocks, the Transit of Venus, and the ‘New Astronomy’ in early seventeenth-century England”, Quarterly Journal of the Royal Astronomical Society 31 (1990),333-571.

Allan Chapman Dividing the Circle (1990) ch 2.

Allan Chapman Jeremiah Horrocks (1994: available from St Michael’s Hoole).

S.B. Gaythorpe, “Horrocks's Observation of the Transit of Venus 1639, November 24, O.S.”, Journal of the British Astronomical Association 47, 2 (December 1936), 60-8.

S. B. Gaythorpe, “Jeremiah Horrocks: Date of Birth, Parentage and Family Associations.” Transactions of the Historical Society of Lancashire and Cheshire,106 (1954), 23-33.

S. B. Gaythorpe “Horrocks' Observations and contemporary Ephemerides” Journal of the British Astronomical Association, 47 (1937) 156-7.

Lawrence Hall, The Birth-place of Jeremiah Horrocks in Toxteth Park  [In Liverpool Central Reference Library].

Lawrence Hall, “Toxteth Park Chapel in the 17th Century” [Rewritten for the Transactions of the Unitarian Historical Society from a paper in July 1933, Copy in Liverpool Central Reference Library].

H. C. Plummer “Jeremiah Horrocks and his Opera Posthuma” Notes and Records of the Royal Society of London, 3,(1940) 39-52.

W. F. Spalding, “A Country Curate” Quarterly Journal of the Royal Astronomical Society, 12 (1971) 179-182.

R. Taton and C. Wilson (Eds) Planetary Astronomy from the Reneaissance to the rise of Astrophysics Part A: Tycho Brahe to Newton (1989) ch.10.

Curtis Wilson “Horrocks, Harmonies and the Exactitude of Kepler’s Third Law” Studia Copernicana,16 (1978) 235-259.

Curtis Wilson “On the Origins of Horrocks’s Lunar Theory”, Journal for the  History of Astronomy, xviii (1987) 77-94.

Albert Van Helden Measuring the Universe (1985) ch 10.

[1] “Horrocks” is an East Lancashire name. He Latinised his name to Horrox for his “official” name eg on the Emmanuel College Register and his Latin manuscripts.

[2] Allan Chapman  Dividing the Circle (1990) p. 26

[3] See John W Shirley (Ed) Thomas Harriot (1974) p. 29

[4] Thus eg the great naturalist John Ray refused to assent to the conditions of the Restoration and was unable to hold a post at Cambridge – this leading to his comparative poverty.

[5] The D.N.B. wrongly stated 1817, but  see  eg S. B. Gaythorpe  Op Cit on Horrocks birth etc.

[6] Thus eg Robert Brickel A Chapter of Romance in Science 1639-1874.

[7] A later date of death of 1652 seems improbable as a will is extant applied in 1644.

[8] These and a lot of other details are in W F Bushell’s “The Keats of English Astronomy”, The Mathematical Gazette, xliii, 343 pp. 1-16.

[9] Lawrence Hall, Toxteth Park Chapel in the 17th Century p. 7.

[10] Lawrence Hall, The Birthplace of Jeremiah Horrocks in Toxteth Park

[11] See eg S B Gaythorpe: “Jeremiah Horrocks: Date of Birth, Parentage and Family Associations.” Trans Hist Soc of Lancashire & Cheshire 106 (1954) 23-33.

[12] W H Watts, “Jeremiah Horrocks and the Transit of Venus of 1639” (1910)

[13] Lawrence Hall, Toxteth Park Chapel in the 17th Century  gives these and other details.

[14] Samuel Clark The Lives of Sundry Eminent Persons in this later Age (1683) cited by Hall.

[15] This was in a retrospective letter to his friend Crabtree.

[16] On all these points see Surtis Wilson in ch 10 of R Taton and C Wilson (Eds) Planetary astronomy from the Renaissance to the rise of astrophysics, Part A: Tycho Brahe to Newton (1989).

[17] These wre the Uranometriam, the Tabulas Perpetuas and the Proggymnasmate de motu Solis.

[18] A R Whatton, Memoir (1859) p. 17.

[19] Albategenius, Alfraganus, J. Capitolinus, Clavii Apolog. Cal. Rom., Clavii Comm. in Sacroboscum, Copernici Revolutioones, Cleomedes, Julius Firmicus, Gassendi Exere. Epist in Phil. Fluddanam., Gemmae Frisii Radius Astronomicus, Cornelii Gemmae Cosmocritice., Herodoti Historia., J. Kepleri Astron. Optica. – Epit. Astron. Copern. – Com. de motu Martis. – Tabulae Rudoplhinae, Lansbergii Progymn. de motu solis., Logomontani Astron. Danica., Magini Secunda Mobiliae.,m Mercatoris Chronologia., Plinii Hist. Naturalis., Ptolemaei Magnum Opus., Regiomontani Epitome, - Torquentum. – Observata., Rhenoldi Tab. Prutenicae – Com. in Theor. Purbachii, Theonis Comm. in Ptolom., Tyc. Brahaei Progymnasmata. – Epistl. Astron., Waltheri Observata.

[20] Horrocks, The Transit of Venus, p. 110.

[21] See eg Richard Westfall Never At Rest (1980) p. 304

[22] See Allan Chapman Three North Country Astronomers (1982) and Dividing the Circle (1990) ch 1.

[23] Bushell Op Cit states that Fogg was mentioned as Curate in 1632 and 1639 but does not state his source, and Chapman  (in “Jeremiah Horrocks and the New Astronomy” Qj Rl Astr Soc (1990) 333-357 note 90) says he cannot find any such references.

[24] At the time of writing, however, it is still repeated on some websites eg one compiled by Professor Richard Westfall of Indiana University.

[25] Jeremiah Horrocks On the Transit of Venus (Tr Whatton, 1859) p. 124.

[26] Allan Chapman Jeremiah Horrocks and Much Hoole (1994) p. 10.

[27] This (from Philosophicall exercises Part 1 para 26)  is quoted in Brickell Op Cit, who rightly concluded that  Horrocks  was a Puritan.

[28] Allan Chapman  “Jermiah Horrocks, the transit of Venus…” J R Ast Soc (1990) 31 333-357.

[29] See eg Allan Chapman Three North Country Astronomers (1982) and Jeremiah Horrocsk (1994)

[30] Chapman “Jeremiah Horrocks, the transit of Venus…” note 2.

[31] Richard Westfall, Never At Rest (1980) p. 542. Westfall has little sympathy with Flamsteed.

[32] O.S. = “Old Style” ie before ten days were added to adjust the calendar in England.

[33] See Albert Van Helden “The telescope and cosmic dimensions” in R Taton and C Wilson  (Eds) Planetary astronomy from the Renaissance to the rise of astrophysics  Part A: Tycho Brahe to Newton

[34] See Albert Van Helden, Measuring the Universe (1985) ch. 8.

[35] His Harmonice Mundi came out in 1619.

[36] Actually he says: “though to illustrious Gassendi, above all others, hail! thou who first didst depict Hermes changeful orb in hidden congress with the sun...etc” (Venus in Transit)  Poetic stuff – modern astronomy journals cannot match it!

[37] Curtis Wilson “On the Origins of Horrocks’s Lunar Theory” Journal of the History of Astronomy,  xviii (1987) 77-94, which also noted Horrock’s notes in his copy of Lansberge’s tables which is in Trinity College Library.

[38] Ibid p. 85

[39] Ibid. pp. 86-90.

[40] Quoted in Ibid. p. 92

[41] Ibid. pp. 92-3.

[42] Newton himself in Principia 2nd-3rd Edns Scholium to Prop. 35 of Book II says “our Horrocks was the first to state that the moon revolves in an ellipse about the Earth placed at its lower focus.”  Kepler had already done this.

[43] See Wilson in Taton and Wilson Op Cit p. 168 etc.

[44] These and other figures are taken from William J Kaufman’s Universe and/or Encyclopaedia Britannica..

[45] Wilson Op Cit p. 167.

[46] Venus in Transit  p. 121.

[47] Venus in Transit p. 213

[48] Van Helden (Op Cit  p. 112) notes that the Belgian Priest Gottfried Wendelin (1580-1667)had written to  Gassensdi in 1635 suggesting planetary diameters proportional to distances, apparent diameters of 28″ from the Sun, and a solar distance amounting to some 58.3 million miles – but this was unpublished!

[49] Quoted in Van Helden Op Cit  p. 112.

[50] Curtis Wilson suggests that Newton probably first read Kepler’s third law in this work [“Horrocks, Harmonies, and the exactitude of Kepler’s third Law”, Studia Copernica 1978, 16, 235-259.

[51] Bushell (Op Cit) reports that Le Gentil was sent to India to observe the 1761 transit but war delayed his arrival. He stayed out there eight years for the next one, but it was cloudy on the day. Coming home he was twice shipwrecked and when he got home found he had been proclaimed dead and his property divided up.  And you thought you had problems!  Others, fortunately for science, had more success.

Information supplied by Paul Marston©

printable versions: pdf, ps

Last updated:
International Astronomical Union University of Central Lancashire Rose