I 



42 ON THE PROPER HE S OF IVIATTEii, 



equally ; though the farther it proceeds the farther it loosens jt. We are 

 told by Mr. Boyle, that two grains and a half of silk, were, on one occasion, 

 spun into a thread not less than three hundred yards long, which is, not- 

 withstanding, a much shorter length than the spider is capable of spinning 

 his web of the same weight. Muschenbroek mentions an artist of Nurem- 

 burg, who drew gold wire so fine that 500 inches of it only weighed one 

 grain ; and Dr. Wollaston has obtained platinum wire as fine as 3 o^^i 

 of an inch.* The thickness of tin-foil is about a thousandth part of an 

 inch ;T that of gold-leaf is less than a two hundred thousandth part of an 

 inch ; and the gilding of lace is still thinner, probably in some cases not 

 more than a milhonth part of an inch ; and there are living beings, visible 

 to the microscope, of which a million million would not make up the bulk 

 of a common grain of sand. Yet it is highly probable, from what has 

 actually been ascertained of the anatomy of minute and microscopic 

 animals, that many of these are as complicated in their structure as the 

 elephant or the whale. 



Gravitation is the common basis upon which all the preceding pro- 

 perties are built, except passivity ; the great principle into which all the 

 rest resolve themselves. Gravitation is the attraction by which bodies of 

 all kinds act upon each other, with a force regulated by the aggregate pro- 

 portion of their respective quantities of matter, and decreasing as the 

 squares of the distances increase. It is a law^ impressed on matter uni- 

 versally, and hence operates alike on the minutest and on the largest masses ; 

 produces what we call weight on earth, or the tendency of heavy bodies 

 to fall towards the earth's centre ; and governs the revolutions of the 

 planets. The five principles which regulate its mode of action, and consti- 

 tute its magnificent code of laws, are thus summed up by M. La Place. J 



1 . Gravitation takes place between the most minute particles of bodies. 



2. It IS proportional to their masses. 



3. It is inversely as the squares of the distances. 



4. It is transmitted instantaneously from one body to another. 



5. It acts equally on bodies in a state of rest, and upon those which, 

 moving within its range, seem to be flying off from its power. 



To a casual observer there are many substances that seem to fly away 

 from the earth, and consequently to oppose this general law. Thus smoke, 

 when extricated from burning bodies, and vapour, when separated from 

 liquids, ascend into the atmosphere ; and a piece of cork, plunged to the 

 bottom of a vessel of v/ater, rises rapidly to the surface. But, in all these 

 phasnomena, the bodies that seem to move upwards merely give way to 

 bodies of a heavier kind, or, in other words, which have a stronger ten- 

 dency towards the earth. Thus smoke and vapour only ascend, because the 

 surrounding air, which is heavier than these, presses downwards and takes 

 their place ; and. the cork rises because lighter than the water into which 

 it has been plunged : but empty the vessel, and the cork will remain at the 

 bottom, because heavier than the surrounding air : and let the smoke or the 

 vapour be received into a vacuum, and it will remain as much at the bot- 

 tom as the cork. 



It was first systematically demonstrated by Sir Isaac Newton, that all the 



Wollaston in Phil. Trans, for 1813, p. 114. Thomson's Annals of Philos. No. U!, 

 p. 224. 



t Davy's Elem. vol. i. p. 379. 



t Exposition dn SystCTne dn Monde, 



