Out of the Shadow of a Giant: How Newton Stood on the Shoulders of Hooke and Halley. John Gribbin
on Thursdays in term time,fn2 in Latin between 8 a.m. and 9 a.m. and the same lecture in English between 2 p.m. and 3 p.m. He seems to have always had the lectures prepared and been available to do his duty, but very often, as his diary records, nobody turned up to listen to them. He also gave the Cutlerian Lectures, officially during the vacations but sometimes on other occasions; many of these were collected and published in 1679. These wandered far from the original brief, which makes them much more interesting to us even if it helps to explain Cutler’s reluctance to pay Hooke.
But that is getting ahead of our story.
The year 1665 was a turning point for Hooke in other ways, but before we discuss the changes in his life that took place in the second half of the 1660s, we should go back to look at his scientific achievements in the first half of that decade.
Some idea of the breadth of Hooke’s activities can be gleaned from a ‘wish list’ he wrote at the beginning of the 1660s of the projects he had in mind:
Theory of Motion:
of Light
of Gravity
of Magneticks
of Gunpowder
of the Heavens
Improving shipping
– watches
– Opticks
– Engines for trade
– Engines for carriage
Inquiry into the figures of Bodys
– qualitys of Bodys
Hooke worked on many of these projects (and others) in parallel.
We can only pick out the highlights, and describe them consecutively, even when two or more of them overlapped chronologically. The extraordinary fact is, though, that Hooke worked on an array of subjects at the same time, while also giving his lectures and doing more experiments at the behest of the Royal Society. But let’s begin with some of his first work for the Royal, using the air pump that Boyle had given to the Society, and which only Hooke could operate effectively. With that tool, he carried out the two duties that were the key to the survival of the Royal Society, a survival that he alone ensured. First, he entertained the Fellows with dramatic demonstrations. The importance of this cannot be overemphasised. It was this kind of showy demonstration that fascinated the more dilettante Fellows and which brought in a flow of subscriptions to keep the Royal afloat, even if that flow was sometimes only a trickle. Secondly, and much more important to us, he carried out experiments that advanced scientific knowledge profoundly.
A good example of Hooke’s skill as a showman, and the way this linked up with his scientific studies, is provided by his work with hollow glass balls. He delighted his audience with demonstrations in which the balls ‘exploded’ as they cooled down after being blown from molten glass, and the way air rushed into them when they were placed under pressure in the chamber (receiver) of the vacuum apparatus and cracked open. Among other things, though, this set Hooke thinking about the strength of arches and other curved structures, so the experiments fed directly into his later work as an architect.
It also seems that Hooke was not afraid to experiment on himself. In his diary entry for 7 May 1662, John Evelyn (himself a Fellow) describes a meeting of the Royal Society attended by the King’s cousin, Prince Rupert:
I waited on Prince Rupert to our Assembly, where were tried several experiments of Mr. Boyle’s Vacuum: a man thrusting in his arme, upon exhaustion of the ayre, had his flesh immediately swelled, so as the bloud was neere breaking the vaines, & insufferable: he drawing it out, we found it all speckled.
There is little doubt that the experimental subject was Hooke himself. Some years later, he built a receiver large enough to sit in, and did so while an assistant pumped the air out. He described how this caused pain in his ears, deafness and giddiness, before he decided enough was enough and the air was let back in. But a discussion of Hooke’s most important work with the vacuum pump can wait until we discuss his great book, Micrographia.
Although he was not afraid to experiment upon himself, Hooke was far more reluctant than most of his contemporaries to experiment on other animals, at least when it clearly caused them pain. At the beginning of the 1660s, nobody knew exactly what the importance of breathing was in sustaining life. One school of thought held that although the circulation of the blood was clearly important, the role of breathing was simply to act as a pumping mechanism, by which the in and out motion of the thorax stirred up the blood and kept it flowing. The idea that something from the air mixed with blood in the lungs and was essential for life was a minority view. In one indecisive experiment at the beginning of 1663, Hooke placed a live chick and a burning lamp in a sealed chamber to see which one lasted longer. The lamp went out, but the chick survived. This, however, neither proved nor disproved the hypothesis. It was not until November 1664 that Hooke, possibly at Boyle’s suggestion, conceived of an experiment on a living dog, which could be dissected ‘displaying his whole thorax, too see how long, by blowing air into his lungs, life might be preserved, and whether anything could be discovered concerning the mixture of the air with the blood in the lungs.’
The gruesome experiment was carried out on 7 November. With the dog cut open and all its organs exposed, unable to breathe of its own volition, air was pumped into the lungs of the dog by a pair of bellows through a hollow cane stuck into a hole in the dog’s windpipe. The experiment was a success, in that the dog lived during it. As Hooke wrote to Boyle on 10 November 1664:
at any time, if the bellows were suffered to rest . . the animal would presently begin to die, the lungs falling flaccid, and the convulsive motions immediately seizing the heart and all the other parts of the body; but upon renewing the reciprocal motions of the lungs, the heart would beat again as regularly as before, and the convulsive motions of the limbs would cease.
But in the same letter, Hooke confessed that although the experiment suggested several other lines of investigation:
I shall hardly be induced to make any further trials of this kind, because of the torture of the creature: but certainly the enquiry would be very noble, if we could any way find a way so as to stupefy the creature, as that it might not be sensible [conscious].
Three years later, Hooke was asked to repeat the demonstration, but initially refused. Two doctors, who were less squeamish about such matters, tried to replace him, but made such a mess of the operation that Hooke, by then an employee of the Royal, was ordered to do it and repeated his earlier success.
At the end of 1662 in another series of experiments, he demonstrated how a hollow glass ball that would float on top of cold water gradually sank to the bottom when the water was warmed, or could be made to ‘hover’ partway up the vessel if the temperature conditions were just right. He correctly suggested that the heat ‘loosened’ the water (that is, reduced its density), which was another step towards an understanding of matter as made up of atoms and molecules. He also invented (at least in principle; we are not sure if he made it) an efficient water heater in which a heated piece of copper at the bottom of a tub of water would heat the whole vessel as the warm, loosened water rose to the top and was replaced by descending cooler water. He had ‘discovered’ convection – but he went too far when he speculated that this might make it possible to manufacture a perpetual motion machine in which the water circulated endlessly through a system of pipes without any further heating once it had been started. More practically, he pointed out that because the cold sea at high latitudes could support heavier ships than the ‘loosened’ water closer to the equator, ships setting out from polar latitudes to the tropics should not be fully laden. Much later, starting in the late nineteenth century, merchant ships were marked with ‘Plimsoll lines’ showing exactly how far they could be safely loaded, depending on the waters they were visiting.
Hooke’s investigations of pressure, density and convection fed directly into another lifelong interest of his: the weather, and the possibility of forecasting the weather. This became a major thread of his work in September 1663, when Wilkins, on behalf of the Royal, asked Hooke to collect daily records of the weather, in the hope that these might reveal patterns