256 PROGRESS OF SCIENCE. 



of) light, heat, electricity, and magnetism. This fluid is 

 "almost infinitely thin and elastic." Now, then, Thomson 

 holds that all that which we know as matter consists of 

 vortices or whirlpools of this ether, which, from their rapid 

 rotating motion, "resist displacement, and therefore show the 

 common properties of hardness and strength in the same 

 way as a spinning-top or gyroscope tends to keep its axis 

 in a fixed position." But whether the molecules or particles 

 of what we know as matter are independent matter, or 

 whether they are ether whirlpools, we know that they keep 

 up an incessant hammering one on another, and thus on 

 everything in space. This atomic bombardment was in the 

 first instance one of Daniel Bernoulli's theories, but in a 

 restricted sense only, for to his mind " the pressure exerted 

 by a gas on the walls of the vessels enclosing it was due 

 to the constant hammering of the walls by the atoms of 

 which the gas consisted." Sir W. Thomson, Helmholtz, 

 and Crookes see in this fact a law which applies universally 

 to all matter throughout space. The future will disclose 

 whether the "vortex theory" is a mere hypothesis or an 

 absolute law. 



1 8 . Cailletet and Pictet LIQUEFIED and solidified 

 GASES hitherto held to be permanent. Faraday was the 

 first physicist who liquefied gases, and soon after him all of 

 them, with the exception of oxygen, hydrogen, nitrogen, 

 carbonic oxide, nitric oxide, and marsh gas, have been 

 liquefied. Cailletet and Pictet succeeded at last (1877-8) 

 in liquefying and even solidifying oxygen, nitrogen, and 

 hydrogen, mainly by intensity of cold. The belief in 

 " permanent gases " was destroyed by these fine results : all 

 substances, according to conditions, were proved capable of 

 assuming the solid, liquid, and gaseous forms a fact which 

 points to the unity of matter. In the course of 1892, Pictet 

 showed that substances subjected to extreme cold "lose 

 the power of chemical combustion, and under this process 

 can be produced in a state of purity hitherto unattainable." 

 In experiments on the compressibility of gases, Cailletet 

 carried the pressure as high as 600, and Petit 650, atmos- 

 pheres. The decisive experiments proving the liquefaction 



