66 THE PHYSICAL SIGNIFICANCE OF ENTROPY 



Step e 



Conversion of the General Expressions in (b) and (c) into more 

 Precise ones by Finding and Inserting the Numerical Value of 

 the Universal Constant k ; Some of the Results 



From the consideration of certain phenomena of radiation 

 PLANCK found 



= i. 34 6(io- 16 ) in absolute C. G. S. system; (27) 

 4o7ro: cleg 



in F. P. S. system, 



where a and b are constants found by experiment while a and ft 

 are exactly known values, mathematically derived. The present 

 accuracy of (27) therefore rests on the accuracy of the experiments 

 from which a and b were found. In discussing Eq. (10) it was 

 pointed out that k was a universal constant, applicable to all 

 physical systems and consequently may be used for the molecular 

 configurations mainly considered in this presentation. But before 

 introducing numerical value of k in the general expressions con- 

 tamed under headings b and c, we will add other numerical 

 values of interest. 



PLANCK gives 2.76(io 19 ) =number of molecules in i ccm. of an 

 ideal gas at freezing-point (o C.) and atmospheric pressure; 



N 

 he also gives for the ratio = 6.1 75 (lo 23 ) = number of molecules 



per nt grams; the corresponding numbers in English units are, 

 approximately, 782 (lo 23 ) =number of molecules in one cubic foot 



N 2.8o(io 26 ) 

 of an ideal gas and = = number of molecules m one 



pound of an ideal gas. Assuming air to be an ideal gas and its 

 " apparent " molecular weight about 28.88, the number of mole- 



