330 DIRECT PROPERTIES OF MOLECULES 118 



not only from the dielectric constant K by means of the 

 relation 



but also from the index of refraction n by means of the 

 analogous formula 



= (- !)/(* + 2), 



which on Maxwell's theory is identical with it. To avoid 

 repetitions I will cite these figures only from Exner's 

 memoir. 



Values of 10 7 s in cm. 



These numbers, too, like those calculated by Dor n from 

 the dielectric capacity, are considerably less than those 

 which were deduced from the coefficients of condensation, 

 and from the deviations from Boyle's law. They agree 

 in magnitude with Dorn's values with striking accuracy, 

 since, almost without exception, they are equal to 

 0-2 millionth of a millimetre. Sulphurous acid is the 

 only exception to this rule in Dorn's table, and in his 

 opinion this is due to inaccuracy in the value of the 

 dielectric capacity used in the calculation ; and since 

 Exner's value is much smaller, we may fall in with 

 Dorn's conjecture. 



We must therefore consider it established that, if 

 electrical or optical measurements are employed in the 

 calculation of the diameter of the molecular sphere of a 

 gaseous molecule, the value 



s = 0-2 millionth of a millimetre 

 is found on the average. On the contrary we find 

 s = 1 millionth of a millimetre 



at least, if we rely upon observations within the domain of 

 mechanics. We should not pretend to see any agreement in 

 these numbers, which vary in the ratio 1 to 5, if we 



