Out of the Shadow of a Giant: How Newton Stood on the Shoulders of Hooke and Halley. John Gribbin
about how the world worked!), that Hooke devoted a great deal of time to developing improved astronomical observing instruments. But making the required accurate observations from the surface of a ship at sea, pitching and rolling in the waves, was totally impractical.
The other way of working out how far east or west of, say, London you were would be to carry ‘London time’ around with you, in the form of a clock or watch set before starting out on the voyage. But that would require a chronometer that could keep time to an accuracy of a few seconds over an interval of weeks or months. And, again, it had to do so on a ship being tossed about on the waves.
In the middle of the seventeenth century, revolutionary developments in timekeeping devices were taking place. Earlier clocks, going back to the fourteenth century, were powered by slowly falling weights, connected to the gears and wheels of the mechanism by cords wrapped around a bobbin-like drum. The drum rotated as the weight fell, and the rate at which the weights fell was controlled by a so-called verge escapement, involving a toothed ‘crown wheel’ which was tugged one step (one tooth) at a time by the pull of the falling weight. When the weight reached its lowest point, it was simply lifted (or wound) back up to keep the clock ticking. These clocks were good for measuring the passage of the hours, provided they were re-set at noon, but did not even measure minutes accurately, let alone the seconds. It was Galileo who realised that the time it takes for a pendulum to complete one swing of its arc depends only on the length of the pendulum, and the Dutch scientist Christiaan Huygens who, in 1656, used this, in conjunction with a traditional verge escapement, to produce the first reasonably accurate pendulum clock. A pendulum 39.1 inches (0.994 m) long takes one second to swing one way, and one second to swing back, at 45 degrees latitude on the surface of the Earth; at one time it was proposed that this length should be used to define the metre (making a metre 39.1 inches), but this was not followed up.fn6 Both Huygens and Hooke set out to improve on these devices, being well aware that no matter how accurate it might be on land, a pendulum clock was hardly the most practical timepiece to have on the heaving decks of a ship.
Hooke’s key idea was to replace the regular swing of a pendulum with the regular pulse of a coiled spring, vibrating in and out. He also devised an improved escapement. The spring-driven mechanism would work in a clock, but, equally importantly, could be made small enough to be incorporated in a watch compact enough to be carried in your pocket.
This is where the historical chronology becomes murky. Hooke certainly had the idea for such a watch by 1660 (the year of the Restoration, when Charles II came to the throne). But had he made a watch to this design by then? Hooke, via Waller, tells us that he had:
Immediately after his Majesty’s Restoration, Mr. Boyle was pleased to acquaint the Lord Boucher and Sir Robert Moray with it, who advis’d me to get a Patent for the Invention, and propounded very probable ways of making considerable advantage by it. To induce them to a belief of my performance, I shew’d a Pocket-watch, accommodated with a Spring, apply’d to the Arbor of the Balance to regulate the motion thereof … this was so well approved of, that Sir Robert Moray drew me up the form of a Patent … [but] the discouragement I met with in the management of this Affair, made me desist for that time.
The discouragement to which Hooke refers is a proposed clause in the patent that says that if anyone else improved upon the design ‘he or they should have the benefit thereof during the term of the Patent, and not I’. It is hardly surprising that Hooke refused to sign away his rights in this way (as he put it, it is easy to add to an existing invention), and there the matter rested until a later dispute, as we shall see, blew up with Huygens.
We know that these events took place – a draught copy of the patent survives. But did they happen in 1660, or a little later? The surviving papers are undated, which doesn’t help. Some historians suggest that it was actually in 1663 or 1664, and that Hooke later fudged the dates in order to strengthen his case against Huygens. The most careful analysis of the papers has been carried out by Michael Wright of the Science Museum in London.fn7 He concludes that Hooke probably mentioned the invention to Moray in 1662, and revealed the details a year or two later, with the invention then being developed further in 1664, with a timekeeper completed in the summer of 1666. We shall never know for sure, and at this distance in time the priority doesn’t matter. What matters is that Hooke certainly did invent a spring-driven pocket watch, unaided, by the early 1660s, while also working as Boyle’s assistant (including the discovery of ‘Boyle’s Law’) and carrying out his own investigations of, among other things, flying, astronomy, and the microscopy that features in the next chapter. Apart from the significance of the watch itself, which was indeed a major development, two points are noteworthy about this story. The first is the way Hooke worked on many projects at once; the second is the connection with the dramatic event of the Restoration. Both would be significant in the next phase of Hooke’s career.
THE MOST INGENIOUS BOOK THAT EVER I READ IN MY LIFE
At the end of the 1650s, England was once again plunged into political turmoil. Oliver Cromwell died on 3 September 1658, and was succeeded by his son Richard, a less competent administrator unable to cope with a Commonwealth that was already in difficulties, with mounting debts and rival factions. In April 1659 Richard was pushed aside and the army took over, raising the prospect of another civil war. Many people who were in a position to do so, Hooke among them, started to make contingency plans. Hooke’s youthful imagination had been caught by the sight of the ships entering and leaving Yarmouth, and he now began to consider life as an adventurer and explorer travelling to the Far East. In May 1659, still not yet twenty-four years old, he read a book, Itenerario, written by a Dutch traveller, Jan van Linschoten, and made notes, which survive, about the kind of life he could expect if he followed in van Linschoten’s wake. He took particular note of the attractions of China, where ‘Schollars are highly esteemed’. But before Hooke’s plans could come to fruition – if they were ever more than a pipe dream – in the spring of 1660 Charles II was welcomed back to England, and the monarchy was restored. A wave of optimism swept the country, and Hooke, from the staunchly Royalist Isle of Wight, abandoned his plans to travel and looked forward to a future in England, where he was securely established with Boyle and had a growing reputation among the wider circle of experimental philosophers. He published his first scientific paper (as we would now call it), on capillary action, in 1661. But by then, the centre of experimental philosophy was shifting from Oxford to London.
More precisely, the scientific activity was centred around an institution known as Gresham College, in the City of London (the edifice known as Tower 42 now stands on the site, between Broad Street and Bishopsgate). In Hooke’s day, the building on that site was a large Elizabethan mansion, once owned by a wealthy merchant, Thomas Gresham. A range of buildings surrounded a square courtyard roughly a hundred yards across. Gresham had died in 1579, and left the income from his investments to have the house converted into a college and to pay for the appointment of seven ‘professors’ in perpetuity. The professors would be provided with an income of £50 a year for life, and rooms in the college, in return for giving lectures in their specialist subjects once a week in term time. The specialist subjects chosen by Gresham were law, physic (medicine), divinity, rhetoric, music, chemistry and astronomy. The professors were also required to be celibate, although as we shall see the interpretation of this term was rather loose. The status of these posts has waxed and waned over the years, but there are still Gresham Professors giving lectures, even though they no longer have a college to live in.
Hooke’s Oxford friend, Christopher Wren, had become the Gresham Professor of Astronomy in 1657, a post he held until 1661, when he returned to Oxford as Savilian Professor of Astronomy. Other experimental philosophers based in, or visiting, London (and crucially including Wilkins, who had become the Master of Trinity College in Cambridge in 1659, but was ejected when the Royalists returned to power, and was now lodging with a friend in Gray’s Inn) used to attend Wren’s lectures, and got into the habit of meeting up afterwards to discuss the topics