The story of astronomical discovery now moves to England where, free from the religious dogma that had bedeviled earlier Italian astronomers, scientists could build on theories such as heliocentrism. At the forefront of these endeavors was the momentous and prolific work of Jeremiah Horrocks, rightly described as “the father of English astronomy.”
The Mersey spreading and presently contracting its stream from Warrington falls into the ocean with a wide channel very convenient for trade, where opens to view Litherpole, commonly called Lirpoole, from a water extending like a pool, according to the common opinion, where is the most convenient and most frequented passage to Ireland: a town more famous for its beauty and populousness than for its antiquity; its name occurs in no ancient writer except that of Roger of Poictou who was lord, as stated of Lancaster, built a castle here, the custody of which has now for a long time belonged to the noble and knightly family of Molineux … This Roger held, as appears in the Domesday book, all the lands between the rivers Ribble and Mersey.
The above description of Liverpool, found in the journal Britannia compiled by historian William Camden (1551–1623), may not sound very much like the sprawling English city of today. The account was written in the 1580s when the population numbered less than a thousand. Early in the following century, when Jeremiah Horrocks (1618–41) was born there, the number of residents had still not reached four figures. When Camden praised Liverpool’s beauty he was not guilty of any form of flattery. By the standards of the times Liverpool was a very clean and attractive seaside town with fine beaches of golden sand. To the north there were virgin sand dunes that stretched nearly 20 miles (32 km) along the coast—much further than the eye could see. To the southwest lay the rural Cheshire peninsula of the Wirral, bounded by the River Mersey and the River Dee. The vista further south showed the snow-capped peaks of Snowdonia in Wales. To the north were the mountains of the Lake District, and on a clear day Snaefell and the mountains of the Isle of Man could be seen from higher vantage points.
Near the castle there was a small natural inlet called the Liver Pool, and it was here that the shipping was accommodated. The pool was fed by a small stream, which ran through a leafy dale known as Dale Street. There was a small bridge giving access to the area “over the pool,” and here a small Puritan community had established itself in an area called Toxteth Park.
The Puritans were tolerated in the England of the 1620s, but because of their unorthodox approach to religion they were not allowed to hold high public office. It was common, therefore, for them to put their energies into trade. Thus James Horrocks was a watchmaker and his wife Mary Aspinwall was the daughter of a watchmaker. This was a time long before the Industrial Revolution; Liverpool and Lancashire had never yet seen a bale of cotton. It is very possible that the Horrocks and Aspinwall families were not only manufacturers of watches, but also dealers who marketed watches made in Nuremberg and other European centers.
When their first son was born in 1618, James and Mary Horrocks christened him Jeremiah. The couple seemed to have a penchant for Old Testament prophets of doom, for when their second son was born three years later they called him Jonah. Both sons were expected to enter the family business, but Jeremiah showed an early interest in philosophy and other subjects beyond watch-making.
At the age of 14, with the help of his family and the local minister, Richard Mather, Horrocks had acquired sufficient knowledge of the scriptures to gain a place at Emmanuel College, Cambridge—the most puritanical of the Oxbridge colleges. Horrocks did not go to Cambridge to study astronomy, however. At this time it was not possible to study the subject at Cambridge. There was no department of astronomy and no professor of astronomy. Indeed, there were very few who knew anything at all about the subject. One of Horrocks’ friends and contemporaries, John Wallis (1616–1703), who matriculated in the same year, arrived to study mathematics. The status of mathematics was much the same as that of astronomy, and Wallis described it:
I did thenceforth prosecute it [mathematics], (at School and in the University) not as a formal study, but as a pleasing Diversion, at spare hours; as books of Arithmetick, or others Mathematical fell occasionally in my way. For I had none to direct me, what books to read, or what to seek, or what methods to proceed. For mathematics, (at that time with us) were scarce looked upon as Academicall studies, but rather mechanical; as the business of Traders, Merchants, Seamen Carpenters, Surveyors of Lands, of the like; and perhaps some Almanac-makers in London. And amongst more than Two hundred Students (at that time) in our College, I do not know of any Two (perhaps not any) who had more of Mathematics than I, (if so much) which was then but little; And but very few, in that whole University. For the study of Mathematics was at that time more cultivated in London than in the Universities.
The same educational shortcomings could be leveled at astronomy. All undergraduates, if they were not of the aristocracy, were expected to train for the church and to become country parsons. The library shelves were straining with theological publications, but there was hardly a single volume on mathematics or astronomy. And yet, by the time he left Cambridge in 1635, Horrocks had read many of the latest astronomical publications and knew exactly what he wanted to do with his life. In Horrocks’ time the total complement of Emmanuel College was between 200 and 300 people. He would therefore have known all of his contemporaries. His closest friends were John Worthington and John Wallis. They both went on to become active members of the Royal Society. Amongst his other acquaintances was Ezekiel Cheever (c.1614–1708), the son of a London spinner educated at Christ’s Hospital School. Cheever entered as a sizar (an undergraduate who received aid from the college for maintenance in return for performing various duties) the year after Horrocks. He left for America in 1637 and became the best-known teacher in the early history of Massachusetts. Another, even better-known, contemporary was John Harvard (1607–38), who later emigrated to the New World. When he died, he left his substantial private library and half of his estate toward the foundation of a new college, later to be called Harvard College.
In 1635, at the age of 17, Jeremiah Horrocks returned to his native Lancashire. He had decided that what he wanted from his life was to be able to study the stars and the planets. He needed books on astronomy to achieve his aims and he also needed instruments. The most important astronomical instrument of the day was the telescope; it had been in use for about 20 years and was beginning to become far more readily available. Horrocks tells us that he purchased a “half crown” telescope, probably at a local fair. He knew that better instruments were available, however, and in May 1638 he wrote that “I have at last obtained a more accurate telescope.”
We now discover that Jeremiah Horrocks was more than simply an astronomer. He was also a poet. The most prominent astronomer before this time who could also claim to be a poet was the philosopher Omar Khayyam (1044–1122). But when it came to putting his thoughts into verse Jeremiah Horrocks was the equal of his Persian predecessor. He was very thrilled with his new telescope and wrote about it thus:
Divine the hand which to Urania’s power
Triumphant raised the trophy, which on man
Hath first bestowed the wondrous tube by art
Invented, and in noble daring taught
His mortal eyes to scan the furthest heavens.
Whether he seek the solar path to trace,
Or watch the nightly wanderings of the Moon
Whilst at her fullest splendour, no such guide
From Jove was ever sent, no aid like this
In brightest light such mysteries to display;
Nor longer now shall man with straining eye
In vain attempt to seize the stars. Blest with this
Thou shalt draw down the Moon from heaven, and give
Our Earth to the celestial spheres, and fix
Each orb in its own ordered place to run
Its course sublime in strict analogy.
During his time at Cambridge, Horrocks corresponded with Herbert Gellibrand (1597–1637), the professor of astronomy at Gresham College in London. Gellibrand, acting in good faith, suggested to Horrocks that he purchase a copy of a book by a Belgian astronomer called Philip Lansberg (1561–1632). Horrocks followed this advice, and he spent the next year trying to fit his observed motions of the planets to Lansberg’s tables. Horrocks met with no success in this endeavor, but in 1636 he befriended a fellow amateur astronomer called William Crabtree (1610–44), who was working at Broughton near Manchester. It was Crabtree who suggested to him that he use the Rudolphine Tables, the work of Johannes Kepler and Tycho Brahe.
The incident illustrates how long it took for scientific works to circulate in the early 17th century. Gellibrand apparently knew nothing of the works of Kepler and Brahe, or he would certainly not have recommended Lansberg’s tables to Jeremiah Horrocks. We now know that the Rudolphine Tables were far in advance of anything else available at that time, but the first people in England to use them were the amateur astronomers Jeremiah Horrocks and William Crabtree. The Copernican system also took a long time to circulate. The Ptolemaic system was still in use by the astrologers at this time, but Horrocks had little regard for it. He soon discovered that the Copernican system was far superior and he put his feelings into verse:
Why should’st thou try, O Ptolemy, to pass
Thy narrow-bounded world for aught divine?
Why should thy poor machine presume to claim
A noble maker? Can a narrow space
Call for eternal hands? Will thy mansion
Suit great Jove? or can he from such a seat
prepare his lightnings for the trembling Earth?
Fair are the gods you frame forsooth! nor vain
Would be their fears if giant hands assailed them.
Such little world were well the infant sport
Of Jove in darker times; such toys in truth
His cradle might befit, nor would the work
In after years have e’re been perfected,
When harlot smiles restrained his riper powers.
In 1639, at the age of 21, Jeremiah Horrocks left his home in Toxteth. He moved to the small village of Much Hoole about 18 miles (29 km) north of Liverpool. Nobody has been able to find the reason for Horrocks’ move. Some have suggested that he was offered the post of curate at the chapel of Much Hoole, while others have suggested that he was employed as a tutor at Carr House in Bretherton. It would be fascinating to discover that the reason was a romantic attachment, but there is no solid evidence to support this theory, either. All we know is that from the summer of 1639 his correspondence to his friend William Crabtree was addressed from Much Hoole and not from Toxteth.
In a survey taken in 1641 the population of Much Hoole was recorded as 235 adults. The choice of residences was limited, with the vernacular-style farmhouses being low and thatched, with smoking peat fires. The dwellings usually had pigs and chickens running in and out of the doorway. They were a far cry from the ideal residence for an educated astronomer. Apart from the church itself the only building in the village suitable for an observatory was Carr House at Bretherton, the home of the Stones family. This was situated about half a mile (about 0.8 km) away from the church. Much Hoole is the last place where we might expect to meet merchants from great trading centers like London and Amsterdam, but there is sometimes a tendency to overplay the isolation of the English village. Above the doorway at Carr House is an inscription in stone that proves the trading connections to be a fact:
Thomas Stones of London haberdasher and Andrewe Stones of Amsterdam marchant hath builded this howse of their own charges and giveth the same unto their brother John Stones: Ano Domini 1613 Lavs.
The Stones family were evidently haberdashers. There is a strong connection between haberdashery, drapery and cloth dealing. Horrocks’ contacts John Worthington and William Crabtree were both involved in the clothing industry.
As Horrocks continued his observations of the planets he discovered to his great delight that Venus seemed to be on course for a conjunction with the Sun—in other words, the planet seemed to be following a path that would take it across the face of the Sun. This was an event so rare that it had never been recorded before. Horrocks knew that his observations might be marred by cloudy skies, so he asked both William Crabtree and his brother at Toxteth to try to make the observation as well. He asked William Crabtree to inform Henry Gellibrand in London about the event, but it appears that the request did not arrive in time.
The year was 1639, and from his calculations Horrocks did not expect the transit of Venus to take place before 3 o’clock on the afternoon of November 24. It appeared from the tables of other astronomers, however, that it might occur somewhat sooner, and in order to avoid the possibility of disappointment, he began to observe the Sun from about midday on November 23. As expected, he saw no sign of the image of Venus. The next day he continued his vigil until he tells us he was “called away by business of the highest importance, which could not with propriety be neglected.” This phrase has given rise to the possibility that he had to give a sermon just as the transit was about to begin. He tells us nothing else about this important business, but since it was Sunday it is reasonable to deduce that he needed to perform a Sabbath duty of some kind. Nevertheless, the task cannot have been too time-consuming for he was back at his telescope again in just over an hour. This would have been just enough time for Horrocks to get to the church, perform his duties and then return to his observations.
When Horrocks returned to his observations he was overjoyed to see that a dark, round spot was already fully entered upon the image of the Sun. It was without doubt the silhouette of Venus that he had been anticipating. He did not want to be accused of seeing nothing more than a sunspot, however—even though that observation alone would have put him in the company of his mentor Johannes Kepler. Thus later, Horrocks went to great lengths in his treatise to explain that Venus appeared on the Sun’s disc as a perfectly circular dark spot. As well as being a perfect circle, the spot moved across the Sun much faster than a sunspot; there was no doubt that he was observing the planet Venus. He measured the size of the dark spot as accurately as he could and he drew it in the exact position it appeared on his image of the Sun. He drew two more images and recorded the times as 3.15 pm, 3:35 pm and 3:45 pm. The image moved by one diameter in the first 20-minute interval, but slightly less in the second interval. Then the Sun set over the Ribble marshes. He knew the value of accurate measurements and he wanted his observation to be as precise as it could possibly be. He was working to angles within seconds of arc. He estimated that the diameter of Venus was 1′ 12″ and he estimated his error was 4 or 5 seconds of arc.
At Broughton, William Crabtree was also trying to observe the event. He had been very unfortunate with the weather, however. The skies were overcast for the greater part of the day and the Sun was not visible. Crabtree had almost given up on the task when, a little before sunset, at about 35 minutes past 3 o’clock, at the same time as Horrocks was making his observation, the Sun suddenly burst out from behind the clouds. Crabtree rushed into his house and he began to observe at once. To his great joy he saw the rare spectacle of Venus passing across the Sun’s disc. In a passage that does much to illuminate the personalities of both men Horrocks recorded the feelings of his friend:
Rapt in contemplation, he stood for some time motionless, scarcely trusting his own senses, through excess of joy; for we astronomers have as it were a womanish disposition, and are overjoyed with trifles and such small matters as scarcely make an impression upon others; a susceptibility which those who will may deride with impunity, even in my own presence, and, if it gratify them, I too will join in the merriment. One thing I request: let no severe Cato be seriously offended with our follies; for, to speak poetically, what young man on Earth would not, like ourselves, fondly admire Venus in conjunction with the Sun. Pulchritudinem divitiis conjunctam? [beauty conjoined with wealth] What youth would not dwell with rapture upon the fair and beautiful face of a lady whose charms derive an additional grace from her fortune?
Jeremiah Horrocks wrote up his account of the transit of Venus, making full use of his careful observations. Firstly he was able to calculate more accurate values for the orbit of Venus and secondly he had a very good estimate of the angular diameter of Venus at the planet’s closest approach to the Earth. But Horrocks went much further than this. Some may say in fact that he went too far, for he used his result to try to estimate the distance from Earth to Venus, and hence calculate the scale of the solar system. To assist him in his endeavors, Horrocks had at his disposal an account of the transit of Mercury, observed a few years before him by the French astronomer and mathematician Pierre Gassendi (1592–1655).
He then formulated what we might call Horrocks’ hypothesis—that every planet has the same angular diameter when it is seen from the Sun. Horrocks knew that some of the planets did not seem to fit his hypothesis, the most obvious being Mars, which was much too small. The hypothesis never reached the status of a law but it was not an unreasonable postulate. It gave a value for what Horrocks called the parallax of the Sun, a measure closely related to what we would call the astronomical unit—the mean distance from the Earth to the Sun.
The table shown overleaf was compiled by Horrocks to enable him to compare his estimate of the solar parallax with those made by other astronomers. In this table Horrocks shows the solar parallax in terms of radius and not diameter, and they are therefore only half of the values quoted elsewhere. An extra column is included to show the distance in millions of kilometers, and the bottom line has been added to show the modern accepted values.
Thus, with the transit of Venus and his estimate of the solar parallax, Jeremiah Horrocks was the first Englishman to contribute significantly to the history of astronomy. But his main contribution was to come. He wanted to find a better method of calculating the orbit of the Moon. Apart from briefly visible bodies such as comets and meteors, the Moon was the fastest-moving object in the sky seen by early astronomers. Many had tried to explain its motion but without success. It was well known that if an accurate theory of the Moon’s motion could be found then it would be an invaluable aid to navigation. Ptolemy had attempted to tackle the task, and his system at least enabled astronomers to forecast an eclipse, but if his theory had been correct then the Moon would have appeared about four times larger than it actually was at some points of its orbit. Horrocks knew that as a first approximation the Earth–Moon system was similar to a sun–planet system. The Earth was at one focus of an ellipse. The ellipse was perturbed, however, by the gravity of the Sun. Horrocks proposed a system whereby the orbit of the Moon oscillated throughout the year, and he set about trying to find the constants of this oscillation. His theory of the motion of the Moon was the most advanced of his time. It was used by the first Astronomer Royal, John Flamsteed (1646–1719), and his successors at the Greenwich Observatory, and it survived for almost a century before a better theory was found.
Unfortunately, Jeremiah Horrocks died suddenly in 1641. Many of his works were lost in the chaos that ensued during the English Civil War (1642–9). Luckily his account of the transit of Venus survived and it was published in 1662. Thereafter, many of his other surviving works also found a wider audience, and his discoveries were acknowledged and acclaimed by the Royal Society as well as by some of the world’s greatest astronomers, including Isaac Newton in his third book of the Principia. John William Herschel was so impressed that he described Horrocks as “the pride and boast of British astronomy.”
Polish-born Johannes Hevelius (1611–87) was one of the leading observational astronomers of the 17th century. He came from a wealthy family of brewing merchants in Danzig, where he was also a town counselor and later mayor of Danzig.
However, his main interest was in astronomy. He built an observatory on the roofs of three connecting houses, the pattern of which closely followed that devised by Tycho Brahe on Hven. As well as numerous other astronomical instruments (all described in his publication of 1673 Machina coelestis) his most notable achievement was the construction of a 45-meter (150 ft) telescope of his own design.
In 1647, after ten years of observation, he produced detailed maps of the Moon, published in his work Selenographia, including diagrams of phases and first estimates of lunar mountain heights. He also made many observations of comets published in Prodomus Cometicus(1665) and Cometographia (1668). During his life he mapped positions for 1564 stars, and these were eventually published posthumously in 1690 by his second wife, Elizabeth Margarethe, in a catalog, Prodomus Astronomiae, and an atlas, Uranographia.