442 Intelligence and Miscellaneous Articles. 



should a vibrating molecule impart energy to the sether without 

 friction or resistance ? The resistance is in fact a measure of the 

 energy imparted. It appears a question whether, if the amplitude 

 of the vibration (or motion which stirs up the sether) of molecules 

 were known, the friction or resistance could not be calculated 

 therefrom. Eor we know the number of vibrations accurately by 

 the spectroscope, and the energy imparted to the sether (or contained 

 in the waves), by the thermopile. To deduce the resistance to 

 passage represented by the act of vibrating or swinging, we only 

 appear to require the amplitude of vibration then. Perhaps a 

 limiting value for this could be approximately arrived at. 



Another cause tending to reduce the velocity of translatory 

 motion possible to the molecules of gases in the accidents of collision, 

 consists obviously in the fact that the internal motion of the 

 molecule (vibration, rotation, &c.) is proportional to the translatory 

 velocity . So if a molecule attained an excessive translatory velocity, 

 it would acquire an excessive vibration. This vibration would soon 

 dissipate the energy in the sether in the form of waves of heat ; 

 and at the next succeeding collisions, the molecule would acquire a 

 relatively slower translatory motion, as it could not retain the 

 necessary vibratory motion (internal motion) which is the essential 

 accompaniment of a very high translatory velocity. So therefore, 

 from all these causes, the speeds capable of being acquired by the 

 molecules of gases in the accidents of their encounters, are probably 

 moderate ; and far less perhaps than might be inferred from the 

 theorem that the velocities vary between zero and a velocity 

 indefinitely great. 



Eefering to a letter received from the late Prof. Clerk Maxwell, 

 I find that — " The number of molecules whose velocity is more than 

 five times the mean velocity is an exceedingly small fraction of the 

 whole number, less than one millionth. But if there were I0 100 

 molecules, many millions of these would have velocities greater 

 than five times the mean, and yet this would produce no appreci- 

 able effect on the whole mass." 



It seems, then, from the above that the number of molecules 

 attaining high speeds is relatively rare. But it appears none the 

 less worth noting distinctly that an indefinitely great velocity 

 would mean a velocity indefinitely greater than the speed of light 

 even. Suppose a few molecules to attain extreme stellar velocities 

 of say 200 miles per second ; it is evident that the friction in the 

 sether (appreciable in the case of meteoric dust) would commence to 

 tell in reducing the velocity. And as for a molecule supposed to 

 acquire the speed of light itself, the molecule would (in traversing 

 the sether) resemble much a cannon ball moving through the air at 

 the normal speed of the air-molecules themselves — about 1600 feet 

 per second — where the resistance to passage is very considerable, 

 so it seems that there are in practice physical conditions limiting 

 the velocities attainable by the molecules of gases ; the resistance 

 to passage augmenting more than in proportion to the velocity. 



