Out of the Shadow of a Giant

by John Gribbin

  Whatever his other problems following the death of his father, Halley was certainly not hard up. It is quite likely that some real estate, probably including the house in Islington, had already been passed on to him while his father was alive, as was the usual practice, but we only know about the personal estate (money and other valuables, including leases on the rented properties) that was the subject of legal action and therefore a matter of record. Halley’s father left £4,000, and the usual procedure was that a third should go to the widow (Joane), a third to be divided by the heirs (which meant it all went to Edmond, as his brother Humphrey was dead), and a third to be divided in accordance with the will. As there was no will, Joane tried to claim this third portion, and Halley fought her claim. When Joane remarried in 1685, further legal action resulted, with the eventual result that the property was divided roughly fifty–fifty. When the dust settled, Halley was left with an income from the various sources we know about amounting to £500–600 a year, with an unknown income from the other assets. He was always comfortably well off. It was in settling some of the financial affairs relating to the estate that Halley went to Alconbury in the summer of 1684, possibly also visiting relatives in Peterborough, and decided to call in on Newton in Cambridge on the way back to London. If not for the mysterious death of his father, that meeting would never have happened.

  We have already described how that meeting led Newton to produce De Motu, and then, at Halley’s urging, to begin work on what became the Principia. But while this was going on, Halley’s situation changed again – once again in a way that would prove advantageous to the publication of Newton’s masterwork – for reasons that are obscure, but seem to have been related to his changed circumstances following his father’s death. We mentioned in passing earlier that Halley became Clerk of the Royal Society. But why? And how? The how is easier to answer than the why.

  It was, as we have seen, part of the reorganisation of the Royal in the autumn of 1685, part of the aftermath of the Hevelius–Hooke controversy, which resulted in the resignation of the Secretaries Aston and Robinson, and their replacement by John Hoskins and Thomas Gale. In January 1686, the Secretary of the Society laid out a set of rules for holders of the post of Clerk, which included the stipulations that he could not be a Fellow, must be unmarried and have no children, must live in Gresham College, and must have no other employment. But after going to the trouble of laying down these ground rules, the President, Samuel Pepys, announced to the Fellows that the choice of Clerk was entirely up to them, and that they could ignore any or all of those suggestions if they chose. They did choose. On 27 January, four candidates, including Halley, put themselves forward. Halley received sixteen votes, more than anyone else, but the others had twenty-two votes between them, so the lowest-ranked candidate dropped out and there was another round of voting. This time Halley received twenty-three votes out of thirty-eight and was elected as Clerk, being formally sworn in on 7 February. Just about the only one of the suggested conditions imposed on him was that he had to resign his Fellowship.

  Why did he take on the job? It was certainly not, as has sometimes been suggested, for the money. He had no need of the £50 annual salary that was offered by the Society. We say ‘offered’ because the Royal was very short of funds and seldom paid him, except in the form of copies of a book, The History of Fishes, which they notionally valued for this purpose at one pound each. The book had been published at considerable expense and had proved hard to get rid of, so they had plenty of copies to spare.fn1 It seems that Halley was motivated by ambition: he wanted to be at the centre of things at the Royal, with his finger on the pulse of science, with an opportunity to influence events, make his own contribution and to be seen doing it. He certainly acted more like a secretary than a clerk, corresponding with scientists across Europe, editing and publishing the Philosophical Transactions at his own expense, and, of course, overseeing the publication of the Principia.

  Halley seems to have had something of the same work ethic as Hooke. Although the post of Clerk was ostensibly a full-time job, he produced a steady stream of his own scientific contributions, both while seeing through the publication of the Principia (itself a project involving a lot of time and effort) and afterwards. In 1686 alone, he worked with Hooke to make observations of occultations of Jupiter by the Moon (part of the project to chart the changing position of the Moon), and produced three scientific papers of significance. One dealt with the relationship between barometric pressure, height above sea level, and changes in the weather. Another picked up on Hooke’s ideas about the circulation of the atmosphere and developed an account of the trade winds, discussing the heating effect of the Sun on atmospheric circulation and the way the resulting pattern of winds was affected by the presence of land masses. The source of his interest in meteorology was mentioned in the paper, referring to his time on the island of St Helena: ‘an employment that obliged me to regard more than ordinary the Weather.’ As well as his own studies, he drew on many sources, including observations made by sailors and descriptions of the winds made by earlier writers, to produce what was in effect the first meteorological chart. The third paper was actually the first publication based on the ideas about gravity that Newton was about to present in the Principia, which Halley had already seen. It focused in particular on the application of the new understanding for gunnery, explaining how projectiles fired from cannon or a mortar moved under the influence of gravity, and how this information could be used to improve the accuracy of artillery. But it was for the publication of the Principia itself that Halley’s early years as Clerk were most significant. The fact that he remained on friendly terms with both Newton and Hooke during and after this project is another testimony to his diplomatic skills.

  Halley’s formal involvement with the project began on 19 May 1686, when the Society passed the resolution that:

  Mr Newton’s Philosophiae naturalis principia mathematica be printed forthwith in quarto in a fair letter; and that a letter be written to him to signify the Society’s resolution …

  It was Halley, as Clerk, who wrote that letter, on 22 May, mentioning that ‘I am intrusted to look after the printing it, and will take care that it shall be performed as well as possible’. But there was one other detail to be tidied up. The Royal still had no money, and on 2 June the Council ‘ordered, that Mr. Newton’s book be printed and that Mr. Halley undertake the business of looking after it, and printing it at his own charge; which he engaged to do.’ So much for any suggestion that Halley needed his salary as Clerk; rather, the Society needed him to subsidise their work. In the event, Halley just about broke even on the project; he may have made either a small profit or a small loss, but nothing dramatic either way.

  The plan was to publish the Principia in three sections, which were called ‘books’ even though they all appeared in a single volume within one set of covers. On 18 June 1686, Halley sent Newton a proof sheet of a few pages of the book, to get his approval of the paper and the type being used. It was in his reply to this letter that Newton wrote the intemperate screed of 20 June, mentioned in Chapter Seven, threatening to withold Book Three. ‘Philosophie is such an impertinently litigious Laddy that a man had as good be engaged in Law suits as have to do with her,’ he wrote. Halley did not act in haste but spent a couple of days mulling things over before composing a masterly response, dated 29 June 1686. He started by reassuring Newton that nobody wanted to take away the credit due to him:

  I am heartily sorry, that in this matter, wherein all mankind ought to acknowledge their obligations to you, you should meet with anything that should give you disquiet, or that any disgust should make you think of desisting in your pretensions to a Lady, whose favours you have so much reason to boast of. Tis not shee but your Rivalls enviling your happiness that endeavour to disturb your quiet enjoyment, which when you consider, I hope you will see cause to alter your former Resolution of suppressing your third Book … These gentlemen of the Society to whom I have comm
unicated it, are very much troubled at it.

  He then dismisses any suggestion that Newton should not be regarded as the ‘Inventor’ of the proof of the inverse square law, and moves smoothly on to business, pushing Newton into a commitment by getting down to the nitty-gritty of publishing details:

  Sir, I must beg you, not to let your resentments run so high, as to deprive us of your third book, wherein the application of your Mathematicall doctrine to the theory of Comets, and severall curious Experiments, which as I guess by what you write, ought to compose it, will undoubtedly render it acceptable to those that will call themselves philosophers without Mathematicks, which are by much the greater number. Now you approve of the Character and Paper, I will push on the Edition Vigorously. I have sometimes thought of having the Cutts [illustrations] neatly done in Wood so as to stand in the page, with the demonstrations, as it will be more convenient, and not much more charge, if it please you to have it so, I will trie how well it can be done, otherwise I will have them in somewhat larger size than you have sent up.

  Newton replied on 14 July, accepting the suggestion about woodcuts and, as we have seen, continued to work on Book Three as Halley had urged. With the first two books in hand, by March 1687 Halley was employing not one but two printers to get it published as soon as possible; apart from the importance of the book, he may have been eager to get it out before Newton changed his mind again. Book Three was delivered to him on 4 April, and swiftly dispatched to the printers. To non-mathematicians this is indeed the most important part of the Principia, and Halley was quick to highlight its importance in a letter to John Wallis, one of his old professors in Oxford. In Book Three, he says:

  is shown the principle by which all the Celestiall Motions are regulated, together with the reasons of the several inequalities of the Moons Motion and the cause and quantity of the progression of the Apogeon and the retrocession of the Nodes. How he falls in with Mr Hook, and makes the Earth of the shape of a compressed spheroid, whose shortest diameter is the Axis, and determines the excess of the radius of the Equator above the semiaxe 17 miles … he gives the reason for the tides … He concludes his book with the theory of Comets, showing that their Orbs are sufficiently near parabolicall; and upon that supposition shows how to find from observation the parabola wherein they move, and gives an exemplar of the Motions of the great Comet of 1680/1, and having stated the Orb from the observations of the Evening Comet, he finds that the comet that appeared in November in the Morning was the same …

  The finished book was published on 5 July, Old Style. Halley received due credit in the preface:

  In the publication of this work the most acute and universally learned Mr. Edmund Halley not only assisted me in correcting the errors of the press and preparing the geometrical figures, but it was through his solicitations that it came to be published.

  Halley’s ‘solicitations’ did not stop there; he was actively involved in promoting the Principia, not least with a lengthy review in the Philosophical Transactions. This might seems today like a conflict of interests, since Halley was the editor and publisher of both the Principia and the Transactions, but it certainly did a great deal to spread the word to people lacking the mathematical sophistication to appreciate Newton’s work first hand. He also gave a copy to the King, James II, somewhat exceeding his authority as Clerk (Pepys, on behalf of the Royal, should have made a presentation of the book in a more formal way), providing a masterly résumé of the main points of the book, pointing out that as a former naval person James would, Halley hoped, be particularly interested in the discussion of tides, and offering to go over anything with the King if ‘by reason of the difficulty of the matter there be anything herein not sufficiently Explained’. This is another hint of Halley’s ambitious nature, self-confidence and willingness for self-promotion, echoing his St Helena project. After 1687, however, with the Principia, including Book Three, safely off his hands, Halley was free to concentrate on his duties as Clerk, and his own scientific work.

  Halley was nearly the equal of Hooke in the breadth of his scientific efforts, and did far more than Newton, who apart from his one piece of brilliance spent far too much time on pointless investigations of theology and alchemy. Halley’s efforts as Clerk, and as editor of the Philosophical Transactions, were also something of a diversion from his own work, but of far more value to science than Newton’s diversions; we shall not, however, dwell on them too much, since any competent administrator could have done the work. What interests us is Halley the scientist, and Halley the explorer.

  Even in 1687, Halley published papers on geometry (again demonstrating his skill as a mathematician), on the evaporation of seawater, and one of the early scientific attempts to explain the biblical Flood. Hooke had suggested that the Flood might have been linked with a wobble of the Earth, which brought the region affected by the Flood under the waters bulging out at the equator. Halley was able to test this idea by comparing astronomical observations made at Nuremberg some centuries earlier with observations made in the seventeenth century. This showed that the latitude of Nuremberg had not changed in historical times. Halley offered an alternative explanation: that the Deluge had been caused by the gravitational influence of a comet passing close by the Earth, which would also have produced ‘a change in the length of the year, and the eccentricity of the earth’s orbit, for which we have no sort of authority’. The idea was wrong, because, as we now know, comets are nowhere near massive enough to have such an effect. But it was a sensible scientific suggestion at the time, and it carried the implication that whatever the physical events leading to the Flood were, they happened much longer ago than the time allowed by the timescale then favoured by the Church. Halley did not spell that out in 1687, but developed his ideas privately, and in 1724 published a paper in which he carried out a detailed analysis of the story in Genesis, where he suggested that the origins of the Flood story were ‘lost by length of time’ and that there must have been ‘a much fuller account of the Flood left by the patriarchs to their posterity’. In other words, the story of the Deluge originated from an ancient verbal tradition, stories passed down the generations since times long past, and was not a divine revelation to Moses. This very modern approach to biblical stories was almost heretical, even in 1724, and demonstrates Halley’s rational thinking.

  On the experimental side, Halley carried out tests to try to determine how the strength of the force of magnetic attraction falls off with distance, but without success. In 1688 he carried out a long investigation of heat, evaporation, the causes of rainfall, and the design of thermometers. He described to the Society a type of fern that he had found on St Helena, and discussed the need of sunlight for green plants to thrive. But alongside the variety of his other activities, Halley was always interested in measurements, particularly astronomical measurements. As well as his own observations, he was involved in the publication of ephemerides (tables of the predicted positions of astronomical objects) in his capacity as Clerk. And, of course, there was always the problem of finding longitude at sea at the back of his mind. By the end of the 1680s, however, Halley and Flamsteed, the other great observer of the skies, had fallen out, and were not on speaking terms. The exact reasons are not clear, but Flamsteed seems to have regarded Halley as an upstart who had designs on his post as Astronomer Royal (quite possibly true). Flamsteed regarded his observations as his personal property, to be hoarded and used as he thought fit, which would eventually lead him into confrontation with the Royal; Halley regarded science as an open book, and was happy to make use of other people’s observations, which Flamsteed saw as theft, or plagiarism. Halley was equally happy for other people to make use of his ideas. Flamsteed, who was a prim and puritanical man, seems also to have taken exception to some aspect of Halley’s private life, which is not otherwise recorded. In 1695, in a letter to Newton, he referred to Halley as having ‘almost ruined himself by his indiscreet behaviour’ and alludes to deeds ‘too foule and large for [discussion
in] a letter’. Tantalisingly, we have no clue as to what those deeds were.

  By the end of the 1680s, Halley was also involved in maritime projects of one kind or another. Exactly when and how these started we do not know, but on 22 March 1689 Hooke mentions in his diary ‘Hally a sayling’ and on 3 April ‘Hally returned’.fn2 Rather than discussing these activities piecemeal, we will describe all Halley’s work at sea, or all that there is a record of, in Chapter Ten. But while we concentrate on the science, keep in mind that there was this other string to his bow, enough for a full career for most men.

  Something for which Halley ought to be remembered, but is seldom mentioned, is that he was the first person to make a scientific estimate of the size of atoms. In the 1690s, the possible existence of atoms was a matter for philosophical debate rather than practical science, but Halley, with his fascination for numbers and statistics, saw a way to cut through the debate. Silver-gilt wire, he knew, was made by drawing out a silver wire from an ingot which had a layer of gold around its circumference. In 1691, he asked gilders how much gold was used in the process, how thick the ingots were, and how thin the layer of gold was. From this information he calculated that the thin layer of gold on the final wire could be no more than 1/134,500th of an inch thick. This layer had to be at least one atom of gold deep, and he worked out that on this basis a cube of gold with sides one-hundredth of an inch long contains at least 2,433 million atoms. This would imply a maximum diameter for each atom of about five millionths of an inch, or 120 nanometers. Halley fully appreciated that in reality the atoms must be even smaller than this, and wrote that they were ‘probably many times lesser, if the united surface of the Gold without Pores of Interstices be considered’ (the modern figure is 0.14 nm). This was a real scientific measurement, made at a time when very few people took the idea of atoms seriously.