j a TABLE 40 {continued) 



PROBABLE VALUES OF THE GENERAL PHYSICAL CONSTANTS 



(2) The Geiger and Scheel " Handbuch der Physik " J contains an article 

 by F. Henning and W. Jaeger on " The General Physical Constants." There 

 is a list of 52 constants, basic and derived, and a statement as to the theoretical 

 and numerical basis of each value. Many approximations and sources of incon- 

 sistency are pointed out, but with one or two exceptions no attempt is made to 

 recalculate data to improve the published values. The Henning and Jaeger 

 article, written in 1926, contains more recent information than the I.C.T. 



Since 1926 much new material has appeared, so that practically every con- 

 stant adopted in the present paper differs more or less in value from that given 

 in either of these two preceding lists. In fact for the great majority of the con- 

 stants considered the adopted value is based primarily on work which has 

 appeared since 1926. In the case of most of the constants, the situation is now 

 much more satisfactory than it was a few years ago. 



The velocity of light in vacuum (c) . — An accurate summary of all numerical 

 results to 1927, in which many errors in the literature are corrected, has been 

 given by de Bray. 2 A good recent account of the experimental methods for 

 measuring c, as well as the numerical results, is that by Ladenburg. 3 



The latest and most accurate direct determination of the velocity of light is 

 that by Michelson, 4 in 1921-1926. When the various sets of results are col- 

 lected under the five different mirrors used, the agreement is quite remarkable, 

 all five results varying only from 299797 to 299795 with a mean of 299796 

 as before. 



c= (2.99796 ± 0.00004) xlO 10 cm • sec." 1 



The velocity of electromagnetic waves may be obtained indirectly from the 

 measured ratio of the electrostatic (es) to the electromagnetic (em) system 

 of electrical units, according to the generally accepted electromagnetic theory 

 of light. The best value of this ratio, which is here denoted by c' , is undoubtedly 

 that found by Rosa and Dorsey. Their final result is the average of a very 

 large number of individual results, taken at different times, under varying 

 conditions, and of remarkable consistency. It seems to Doctor Birge that about 

 one part in 30000 is a very conservative estimate for the probable error, giving 

 ^ = 2.997 1 ±0.0001. 



This result is in terms of international electrical units. Henning and Jaeger 8 

 show that, to obtain the true ratio between the es and the em system, in absolute 

 units, the result of Rosa and Dorsey must be multiplied by p 1/2 , where one int. 

 ohm = p abs. ohm. According to a subsequent discussion, p = 1 .0005 1 ± 0.00002. 

 This gives a corrected value of c'= (2.9979 ±0.0001 ) X io 10 cm • sec -1 . It is in 

 beautiful agreement with Michelson's recent value of c. 



henceforth denoted by H.P. 2 Nature, 120, 602, 1927. 3 Handb. der Exp. Phys., 18, 1, 

 1928. " Astrophys. Journ. 65, 1, 1927. 5 Bur. Standards Bull., 3, 433, 1907. 6 H.P., 2, 507. 



Smithsonian Tables 



