Lectures de Potentia Restitutiva, or of Spring

Namely, to examine whether bodies at a further distance from the center of the Earth did not lose some of their power or tendency towards it This refers to the force of gravity. I proposed it as one of the experiments to be tried at the top of the Peak of Tenerife A high volcanic mountain in the Canary Islands often used for atmospheric and gravitational experiments in the 17th century, and attempted the same at the top of the Tower of St. Paul's Cathedral before it was burned in the late Great Fire The Great Fire of London in 1666. I also tried it at the top and bottom of St. Peter's Abbey in Westminster Westminster Abbey. However, because these locations were only a small distance from the Earth's surface, I was not able to perceive any clear difference with certainty. I also proposed that the same should be tried at the bottom and at various levels of deep mines; Dr. Henry Power original: "D. Power"; a physician and early experimenter with the microscope and barometer did make some trials for that purpose, but because his instruments were not good, nothing could be concluded from them with certainty.

These are the phenomena of springs and elastic original: "springy" bodies. Just as these have not yet been reduced to mathematical rules by anyone that I know of, so too have all attempts to explain the reason for their power—and of elasticity in general—been very insufficient.

In the year 1660, I printed a short book original: "Tract" which I called An Attempt for the Explication of the Phenomena, etc., of the Rising of Water in the Pores of Very Small Pipes, Filters, etc. At that time, I was unwilling to publish this theory because I thought it might be harmful to my design for watches, for which I was then obtaining a patent. I only hinted at the principle which I supposed to be the cause of these phenomena of springs on page 31 of the English edition, and on page 38 of the Latin edition (translated by Michael Behem and printed at Amsterdam in 1662). I deferred the further explanation of it until another opportunity.

The principles I mentioned then I called by the names of Congruity and Incongruity of bodies. I promised a further explanation of what I meant by those terms on some other occasion. I shall here only explain as much of it as is necessary to explain this present phenomenon.