TRANSACTIONS OF SECTION A. 499 



which we know atoms to possess. It was originated by Sir William Thomson, 

 whose conclusions, based on the reasearches of Helmholtz on fluid motion, may he 

 briefly summarised. 



According to this view the whole of space is filled with a frictionless fluid, and 

 material atoms are portions of this fluid, having a species of rotational motion, 

 which, as Helmholtz proved, must continue for ever. 



The best analogy to this universal plenum and to these vortex atoms is the 

 behaviour m an atmosphere of « smoke-rings," such as may be blown from the 

 mouth of the smoker of tobacco, from the funnel of a locomotive, or from the 

 niouth of a cannon. Such smoke-rings have remarkable properties, which are 

 due, not to the smoke, which merely renders them visible, but to their internal 

 motions. 



Such "vortex rings" can travel with great rapidity. They can vibrate, they 

 can rebound from each other with perfect elasticity, and, supposing that such action 

 takes place in a frictionless fluid, they would be' no less indestructible than un- 

 beatable by mechanical means. 



It is also well known thatLe Sage of Geneva conceived a kinetic theory of gravi- 

 tation, which has been adopted by Sir William Thomson. According to Le Sage, the 

 whole of space is filled with small particles, which he calls ultramundane corpuscles, 

 flying with enormous velocity through every point of space in every direction, 

 lhese penetrate even the void spaces between atoms, so that of those which shower 

 upon the earth perhaps not more than 1 in 10,000 have their velocity diminished 

 by collision. The others pass right through the earth. Owing to these collisions, 

 however, a smaller number of ultramundane corpuscles are to be found moving in 

 the direction from the earth than towards it. Thus the earth acts as a shield, 

 protecting surrounding bodies from the shower of ultramundane corpuscles in that 

 direction. . Hence the moon, and bodies on the earth's surface, are battered by ultra- 

 mundane corpuscles most in the direction towards the earth. This force, driving 

 bodies towards the earth, explains terrestrial gravitation. Similarly, all bodies are 



Q™ V w-i t i° War ™ each ° ther with a force var yi n g as the product of the masses, 

 bir William Thomson supposes ultramundane corpuscles to be vortex rings with no 

 hole m the centre and elongated, like a serpent rushing forwards and always turning 

 inside out, spitting its inwards out at its mouth, and absorbing its skin at the other 

 end. Collisions with vortex atoms would not result in a destruction of velocity 

 and consequent enormous generation of heat, but energy of translation is con- 

 verted into some other form of energy, perhaps energy of vibration. 



However artificial these hypotheses may appear at first sight, the more they 

 are studied the more satisfactory are they. They are the only suggestions of the 

 kind which are in any way tenable, and they serve at least the part of working 

 hypotheses Some remarkable and unforeseen consequences follow from the co- 

 existence of such vortex atoms and ultramundane corpuscles as Thomson has con- 

 CeiV i 6 w G followiu ? facts seem t0 follow from the laws of hvdro-kinetics :— 



1. When a body is heated, and the vortex atoms are rushing about, their 

 mutual collisions originate vibrations in themselves which, when they are free, 

 have a definite period, or periods, depending upon the nature of each vortex atom. 

 _ J. When an ultramundane corpuscle passes such a vibrating atom, the succes- 

 sive approaches and recessions of the atom to and from the corpuscle impress upon 

 tnat corpuscle a wave-form whose dimensions depend partly on the velocity of the 

 corpuscle, partly on the vibrations of the atom. 



a -l'i T heD a C0 FP uscle so stamped continues its progress through the frictionless 

 fluid before mentioned, the position of the wave-marks remain fixed relatively to 

 the corpuscles, without being affected by its internal motions. 



4. II such a marked corpuscle in its flight passes the neighbourhood of a cold 

 atom, i.e., one which is not vibrating, and if that atom be capable of vibrating in 

 tne same period as the original atom which impressed the wave-trace, then the 

 wave-trace on the corpuscle will, on passing the atom, cause it to vibrate in the 

 same manner as the original atom. 



The phonograph supplies a happy illustration of these processes :— 



J . When the membrane, with needle attached, is vibrating we have the analogue 

 of a hot atom. b 



K K 



