374 Dr. A. Naumann on the Velocity of Atomic Motion. 



But, according to Clausius*, the meanf velocity of the pro- 

 gressive motion of any gas-molecule is 



w = 485 m A/?Z^±4 

 V 273 d 



where t denotes the temperature, and p the specific gravity of 

 the gas in question. The absolute zero, which is here taken as 

 273° C. below the freezing-point, is, as was remarked above, more 

 accurately 274°*6 C. below the freezing-point ; accordingly we 

 have for the velocity of the atoms, 



p«= 0-8165 .485 m \/ 274 ' 6 ±* (1) 



For 0°, the equation becomes 



/I 396- 



Hence we get the following velocities for the motion of the 

 atoms at 0° : — 



Velocity of 

 Velocity of a molecule 



z> =0'8165.485 m 





an atom 



(Clausius). 





metres. 



metres. 



For Oxygen 



. 376 



461 



For Nitrogen . 



. 402 



492 



For Hydrogen . 



. 1506 



1844 



Now of what kind is the motion of the atoms ? A movement 

 corresponding to that of the molecules, or, so to say, an indefi- 

 nite wandering about within the sphere of their molecules, is in- 

 admissible, if only on the ground that, if such were the case, 

 metameric gases must be continually changing one into another, 

 and we should obtain, by cooling, liquid mixtures of all possible 

 metameric compounds, which is well known not to be the case. 

 We are thus compelled to suppose an oscillatory movement of 

 the atoms towards and away from each other. In order that 

 this may occur, the mutual repulsion of two atoms must dimi- 

 nish, as the distance between them increases, more rapidly than 

 their mutual attraction. The position of equilibrium, then, is the 

 distance at which attraction and repulsion are in equilibrium and 

 mutually neutralize each other. The velocity as above determined, 

 which is to be taken into account in calculating the vis viva of 

 the motion of an atom, is the velocity with which an atom passes 

 its position of equilibrium, or its so-called intensity of vibration. 

 As the temperature rises, the velocity of an atom in passing its 

 * Pogg. Ann. vol. c. p. 377 (1857). t Ibid. p. 372. 



