282 THE REALITIES OF MODERN SCIENCE 



10 10 and for oxygen approximately half as many col- 

 lisions per second under standard conditions. 



The mean translational kinetic energy of a mole- 

 cule per degree is found by the equation w = 3R/2N as 

 3(83.2) X10 6 /2(60.65)X10 22 or 2.06XH)- 16 ergs. 



As an illustration of the variations in the determi- 

 nation of molecular magnitudes and also of the re- 

 markable consistency of the values obtained by widely 

 different methods, consider the following table l : 



TABLE II 



Phenomena Observed N+1Q 22 



Viscosity of gases (Van der Waals's equation) 62. 



Brownian Movement Distribution of Grains .... 68.3 



Brownian Movement Displacements 68.8 



Brownian Movement Rotations 65. 



Brownian Movement Diffusion 69. 



Irregular Molecular Distribution Critical Opalescence . 75. 



Irregular Molecular Distribution The Blue of the Sky . 55. 



Black Body Spectrum 64. 



Charged Spheres (in a gas) 68 



Radioactivity Charges Produced 62.5 



Radioactivity Helium engendered 64. 



Radioactivity Radium Lost 71. 



Radioactivity Energy Radiated 60. 



Millikan's Value Charged spheres in a gas 60.65 



The agreements are more remarkable than the dis- 

 crepancies when we stop to realize what an enormous 

 number of molecules there are in a mole. The funda- 

 mental assumptions of the kinetic theory cannot be 

 doubted in the light of this evidence. This does not 

 mean, however, that certain assumptions which are 

 sometimes made for convenience of mathematical 

 analysis are verified. For such analysis it is usual to 

 assume that the molecules behave like hard elastic 



1 From Perrin's "Atoms" except for the addition of Millikan's 

 value and the value obtained from the blue of the sky. 



