From the beginning Newton was dissatisfied with what was at that time called ‘cohesion’.  What is it that makes the corpuscles cohere together in individual forms in the way that they do?  What moves them into the geometric shapes that they take?  Both Descartes’ view that it was the indirect, and Boyle’s view that it was the direct, action of God in the world offended against Newton’s Arianism, and he began to search ancient texts for evidence of an active cosmic force, close to the divine but not itself God, that makes fundamental elements cohere in the forms that they do.  He thought that he had found evidence of the prisca sapientia’s  knowledge of such a force in the ancient Stoic doctrine of pneuma.  The Stoics believed that there was a world breath, made of air and fire.  It animated the whole living cosmos, which was one single organism, a giant living whole, moulding all material things into the shapes that they are and breathing life into animate beings.   This breath of life escapes from a living body at the time of death and allows the body to return to its constituent parts, out of which the pneuma will create new forms.  Although always material, the pneuma becomes subtler and finer as the scale of being is ascended, increasingly composed less and less of air and more and more of fire, until it approaches the pure fire which is the first of all the manifestations of the hidden divine. The presence of this active creative force is demonstrated both in the beauty and grandeur of the universe and in its rational order.  Although the Stoics were determinists, their deity was immanent and active in the cosmos through its first agent, the pneuma, and all things were guided by the benign care of a merciful providence.  Here was a description of the very Arian agent of the divine, in a preserved fragment of a lost ancient religion, that Newton was looking for.


Newton’s confidence in Descartes’ corpuscular theory was further shaken by two developments in the early 1670’s.  The first occurred when the astronomer Edmund Halley persuaded the obsessionally reluctant Lucasian Professsor to write a paper for The Royal Society, assessing the significance of Halley’s observational confirmation of Kepler’s eliptical planetary orbits through his new and powerful telescope at Greenwich.  Newton responded with De Motu Corporum in Gyrum.[1]  Kepler’s original calculations had been purely theoretical and had taken no account of any medium through which the planets might pass.  Still accepting the universal assumption of mid-seventeenth century science that there was a corpuscular ether pervading the universe, Newton expected that he would have to adjust Kepler’s equations to take account of it, in order to bring the theoretical predictions into line with the actual observations.  To Newton’s surprise, the equations and the observations fitted exactly.  There was no corpuscular drag slowing the planets.


The second event was an air pump experiment that Newton conducted himself with an air chamber that he had himself constructed.  Realising that Boyle’s void within the void experiment had not necessarily shown that ether as well as air had been removed by the air pump, Newton devised a further experiment designed to resolve the question.   A topic much debated in seventeenth century physics was why, if there was perpetual motion of corpuscles, pendulums that had been set in motion eventually came to a halt.  It was thought to begin with that this was caused by the resistance of the corpuscles in the air.   But when Boyle removed the air from his air chamber the pendulum still slowed and then halted.  So it was then presumed that there was ether that penetrated all matter, including that of the pendulum, and interacted with it to slow down and eventually stop the pendulum’s motion.  Newton now devised an experiment to find out if this were so.  He first removed the air from the chamber and allowed the pendulum to halt as normal.  He calculated that if ether did indeed penetrate matter, the more matter there was the more it would be penetrated.  If weights of lead were added to the bob of the pendulum, then the greater the weight of the lead the more ethereal corpuscles there would be, and the more quickly should the pendulum slow.  His experiments showed that there was no difference.  It was looking more and more as if the corpuscular ether did not exist.  But if it did not, then how to explain gravity?  In the prevailing theory the weight of the corpuscles caused them to fall through the ether.  In dense solid objects they became so numerous the object was pulled down to the ground.  The motions of the planets were also explained by the corpuscular theory    In the orthodox teaching planetary motion, like all other motion, was essentially in straight lines.  It was the resistance of the ether that bent these straight lines into elliptical orbits.  But nobody dreamt that stones falling to the ground and the planets rolling in their courses were in any other way connected.  

[1] Michael White 1998 Isaac Newton: the Last Sorcerer. London . Fourth Estate.  Pp. 210.11


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