Manuscript of the Month April 2015 a calculation of the Great Eclipse of the Sun, by William Whiston, April 1715

Manuscript of the Month

April 2015
A Calculation of the Great Eclipse of the Sun, by William Whiston, April 1715
On 20th March this year, large swathes of the British Isles were plunged into near darkness by a solar eclipse. Scientists deployed mini satellites to track its exact path, while millions of amateur stargazers resorted to specially adapted glasses, pin-hole projectors or even kitchen colanders in a bid to witness the phenomenon for themselves. Live streaming also enabled many others to watch the drama unfold via their computer, tablet or smart phone. Three hundred years ago, things were very different. But a total solar eclipse in 1715, the first London had seen for 500 years, aroused its fair share of interest amongst scientists and citizens alike.

The weeks and months leading up to the 1715 eclipse saw the publication of various broadsheets devoted to the subject. Some sought to reassure the public. ‘The Black Day or a Prospect of Doomsday,’ for example, despite its cataclysmic sounding title, promised readers: An Eclipse of the Sun…proceeds only from natural Causes; and is nothing else but the direct Interposition of the Body of the Moon between our Sight and the Sun. Others, though, played on fears that the eclipse was a bad omen. Astrologers in particular delighted in reminding people of the calamities that had befallen the country in the wake of previous eclipses. For had not the execution of Charles I (1649), the Great Plague (1665-66) and the Great Fire of London (1666) all followed hard on the heels of similar events? In which case, therefore, this latest eclipse could well be viewed as a judgement on the newly crowned King George I, whose arrival in England from Hanover a few months earlier had re-ignited an earlier Jacobite threat. Above all, however, there was a desire to educate and explain. Fleet Street publishers J Nutting and Thomas Taylor issued an illustrated explanation of the upcoming eclipse which, they insisted, would make it plain to the meanest Capacity, while John Senex, based at the Globe in Salisbury Court, Fleet Street, published at least three accounts: one by mathematician Edmond Halley and two by William Whiston.
William Whiston (1667-1752), son of a Leicestershire clergyman, had studied mathematics at Clare College, Cambridge, before entering the church. After serving several years firstly as chaplain to the Bishop of Norwich and subsequently as vicar of Lowestoft, he returned to Cambridge in 1701. A short time later, Whiston succeeded Isaac Newton as Lucasian Professor of Mathematics and his future seemed assured. But by 1715 his circumstances had shifted dramatically. The loss of his professorship in 1710, precipitated by his outspoken religious views, had been followed by five long years of legal wrangling as he sought to defend himself from charges of heresy. During this time, Whiston had been reduced to scratching an uncertain living by means of lecturing, writing and teaching. The upcoming eclipse, therefore, was doubly attractive to him, offering as it did both the prospect of studying a rare scientific event at first hand and a heaven sent opportunity to bolster his finances. Like Halley, Whiston produced a ‘Calculation of the Great Eclipse’ (pictured), in which he described the eclipse’s construction and endeavoured to predict its path, its timing and its extent. Unsurprisingly, given the limits of knowledge the two men were working within at the time, Whiston’s and Halley’s predictions differed somewhat. Whiston too shied away from incorporating a map illustrating the eclipse’s likely path into his Calculation, as Halley had done, claiming, the nature of the Construction does not admit of that Projection. Instead, Whiston contended, Such a Thing cannot be truly represented any other way than by the Copernicus, a ‘Universal Astronomical Instrument’ of his own devising, available in three sizes at a cost of four, five or six guineas. At the same time, he took care to remind readers that copies of his ‘Astronomical Lectures’ and his edition of Euclid’s ‘Elements of Geometry’ were also available for purchase.
Like Whiston, Edmond Halley was fully alert to the unrivalled opportunities for research offered by the eclipse. In particular, Halley hoped to be able to measure the eclipse, which would enable him to predict the trajectory and timing of future ones more accurately. It was with this object in mind that he had had the map so derided by Whiston produced. In an early example of crowdsourcing, copies of Halley’s map were sent to fellow enthusiasts across the country along with an earnest plea for them to observe what they could: but more specially to note the Time of Continuance of total Darkness, which, Halley believed, required no other Instrument than a Pendulum Clock with which most Persons are furnish’d. (Royal Society, Phil Trans 1714-16 29, 245-262)
Daybreak on 22nd April (3rd May by today’s calendar) found Halley ensconced on top of the Royal Society’s headquarters in Crane Court, just around the corner from Hoare’s Bank, armed with a six foot telescope, a quadrant and a pendulum clock. With him were numerous other Society members, two bank customers, the Earl of Abingdon and the Lord Chief Justice, the latter of whom was to prove remarkably adept at measuring and calculating, and representatives from several European scientific societies. At six minutes past eight, Halley detected a small dent on the western most edge of the sun. Over the next hour he and his fellow watchers observed, calculated, noted and observed again as the sun steadily disappeared behind the moon and a cloak of cold damp darkness gradually enveloped them. Finally, at 9:09:17, Halley pronounced the eclipse complete: This Moment was determinable with great nicety, the Sun’s light being extinguish’d at once; and yet more so was that of the Emersion, for the Sun came out in an Instant with so much Lustre that it surprized the Beholders, and in a Moment restored the Day.
To Halley’s relief, the weather that morning behaved impeccably. There was little wind and no cloud to thwart his study, although almost as soon as the eclipse ended the sun retreated behind thick cloud for much of the rest of the day. Other observers reported mixed fortunes however. The astronomy professors at England’s two universities saw little of the eclipse – heavy clouds over the Oxford skyline deprived Dr Keill of all but its conclusion, while Rev Cotes’s view at Cambridge was, according to Halley, opprest by too much Company. As Halley had hoped, though, accounts and calculations were forwarded on to him from other parts of the country. Many he discarded, doubting their accuracy, but others he judged reliable enough to be depended upon, not least those submitted by the Rector of Wanstead, Essex; by John Bridges, Treasurer of His Majesty’s Revenue of Excise, who had based himself near Kettering, Northamptonshire; by the Ashmolean Museum’s Keeper, John Whiteside, who had plumped for a spot close to Hitchin, Hertfordshire, and bank customer Theophilus Shelton of Pontefract.
Whiston too emerged from the eclipse with some degree of success. A series of well-attended public lectures, for which he charged a guinea a head, along with the proceeds from the sale of his ‘Calculation,’ quickly succeeded by a second more elaborate edition, and presents from various benefactors, earned him nearly £120 (c.£16K today): Which in the Circumstances I then was, and have since been, destitute of all Preferment, was a very seasonable and plentiful Supply: And, as I reckoned, maintained me and my Family for a whole Year together. (Memoirs of the Life and Writings of Mr William Whiston, Vol 1, London, 1749, pg 239)
To the joy of scientists and money-makers alike, Britain’s skies would play host to three more major eclipses during the first half of the eighteenth century: in 1724, 1737 and 1748. Each was preceded by a frenzy of lecturing and publishing, as well as the sale of glasses, smoked or otherwise, assorted scientific instruments and countless tips on how to how to observe the eclipse safely. For the 1748 eclipse, the London Magazine (in an article so popular it had to be repeated) advised readers to make a pin-hole projector or hold a piece of glass over a candle until it was entirely blackened: and then the eclipse may be viewed through it, either with the naked eye, or through a telescope. (The Scots Magazine, 6th May 1748) Telescopes were naturally the preserve of the wealthy, but at least one member of the Hoare family was interested enough to take the plunge. In November 1736, just a few months before the 1737 eclipse, Richard Hoare (1710-54) bought a six guinea telescope from Fleet Street instrument maker Thomas Wright. A decade later, in September 1747, he purchased a second one from Wright’s successor, Benjamin Cole. And the following summer, perhaps with the upcoming eclipse in mind, he instructed Cole to send a three foot telescope to a Mr Morris at Bath on his behalf.
Whiston too made the most of these additional eclipses. That of 1724 prompted a new broadsheet, ‘The Calculation of Solar Eclipses Without Parallexes,’ in which he alerted readers of his soon-to-be-produced Orrery, for the Explication of the Motions of all the Planets and Comets, as well as an improved Copernicus, for the easy Discovery of all Solar Eclipses whatsoever, from the Beginning of Astronomy, till AD2000. And in the run up to the 1737 eclipse, Whiston embarked on a course of fifteen weekly astronomical lectures at no less than three different coffee houses, including the Temple Coffee House on Fleet Street, at a cost of a shilling per lecture or a guinea for all fifteen. Between times he was equally busy, devising new scientific instruments and maintaining a gruelling schedule of lectures, publications and re-publications on all manner of astronomical, mathematical and theological subjects. The year 1729, for example, found him giving lessons in mathematics at Grigbsy’s Coffee House behind the Royal Exchange, as well as weekly lectures on astronomy and periodic ones on his ‘Models of the Tabernacle of Moses and the Temples of Jerusalem.’ Nor did he neglect his other great passion, one that had taxed his mind – and the minds of many others – for decades: the Longitude problem. Whiston’s proposed solutions – dipping needles, refracting and reflecting telescopes, the observation of eclipses, coastal surveys and the exploding of fireballs – attracted some support but little success, although the last must have gone some way towards enlivening his lectures. Audiences in 1742, for example, were promised: nine Lectures, concerning Navigation, and the Discovery of the Latitude and Longitude at Sea, including the Survey of the Coasts, and his [Whiston’s] Method of giving Signals to Ships at Sea, by Balls of Fire to be thrown up during those Lecture Nights, at Eight o’Clock, when the Air is clear, out of a Demi-culverin, from Shooter’s Hill; with the Way of observing them, and finding the Ships Distance from them. (Daily Post, 4th Jan 1742)