go TABLE 40 (continued) 



PROBABLE VALUES OF THE GENERAL PHYSICAL CONSTANTS 



In the later work ( 1906 to date) the current, measured in abs. amp., usually 

 with a current balance, is sent through an int. ohm resistance, using a Weston 

 normal cell. From the known current in abs. amp. and the known resistance 

 in int. ohms, one obtains the e.m.f. of the Weston cell in semiabsolute volts. 

 By eq. (11) the ratio of this result to the e.m.f. in int. volt (v), (1.01830 by 

 definition), is r/p, evaluating only r/p, and not q. 



The value of the e.m.f. of the Weston cell, in semiabs. volts, the assumed 

 corresponding electrochemical equivalent of silver per abs. coul., and the 

 true resulting value of r/p, are listed by Henning and Jaeger. 1 Omitting a 

 probably less accurate value by Guthe, the remaining four values range from 

 1.00006 to 0.99989. Henning and Jaeger give correctly as 1. 01822 semiabs. 

 volts the Rosa, Dorsey and Miller 2 value of the e.m.f. of the Weston cell, but 

 misquote and use in their averages the resulting E Ag and r/p, giving 0.99995 

 for r/p in place of the true 0.99992 ( = 1.01822/1.01830). Using 0.99992, the 

 unweighted average of the four investigations 3 is r/p = 0.99995. The Bureau 

 of Standards 4 considers only (a) (c) and (d) of reference 3 and gives 0.99991 

 as the best average value of r/p. The I.C.T. value (0.99990) is based on (a) 

 and (d) only. Henning and Jaeger 1 take the unweighted average of all four 

 values, and Doctor Birge has done the same, since there seem to be differences 

 of opinion as to the relative weighting of these four values. It is very probable 

 that (c) should be given a relatively lower weight; the final average is 

 fortunately not changed. 



The next question concerns the equality of r/p and q. Rosa, Vinal and 

 McDaniel 5 determined the e.m.f. of the Weston cell as 1.01827 int. volt (a), 

 by using a silver voltameter and an int. ohm resistance. Hence by eqs. (4) and 

 (8), knowing 1.01827 int. volt (a) = 1.01830 int. volt (v), pq/r— 1.01830/ 

 1.01827=1.00003. Hence 9=1.00003 r/p. These investigators naturally as- 

 sumed r/p = 0.99992, for reference 3 (d). Hence 9 = 0.99995. This is the 

 figure misquoted as r/p, by Henning and Jaeger. 1 



The result indicates that q differs from r/p by 3 parts in io 5 , and that, to 

 agree with the primary int. units, the Weston cell should have been taken as 

 1. 01 827 int. volts. But at the Reichsanstalt,* the corresponding quantity was 

 found, in 1908, to be 1.01834 int. volts, and in 1922, 1.01831. The average 

 of these three results indicates that the accepted value of 1. 01830 int. volts is 

 correct within limits of error. In other words, q = r/p, and one int. volt 

 (a)=one int. volt (v). This agrees with the view of Henning and Jaeger. 7 

 The relative values of q and r/p adopted by the I.C.T. are based directly on 

 the work of the Bureau of Standards. 2, 6 



'H.P, 2, 500, Table 6. a Bur. Standards Bull., 8, 269, 1912. 3 (a) Ayrton, Mather, 

 Smith, (N.P.L.) 1908, r/p = 0.99989, (b) Janet, Laporte, Jouaust, 1908, 1.00006, (c) Haga, 

 Boerema, 1913, 0.99994, (d) Rosa, Dorsey, Miller (Bur. Standards), 1912, 0.90992. * Bur. 

 Standards Circ. 60, 38, 1916. ° Bur. Standards Bull., 10, 475, 1914. 8 Z. Instrument., 28, 

 327 and 353, 1908; ibid., 42, 221, 1922. T H.P., 2, 501. 



Smithsonian Tables 



