g5 TABLE 40 (continued) 



PROBABLE VALUES OF THE GENERAL PHYSICAL CONSTANTS 



Duane, Palmer, and Yeh used a known potential (int. volts) and measured 

 the angle 6 at which the ionization suddenly started (or stopped). This gives 

 the critical ionization frequency corresponding to the given voltage. Wagner 

 used known wave lengths varying the voltage for a given wave length, until 

 ionization suddenly began (or ceased). Both methods involve the calcite 

 grating space d. On page 91 the absolute wave lengths of rays were used to 

 evaluate d', the true grating space ; d! was then used with other known con- 

 stants to evaluate the electronic charge e. In this section we use the finally 

 adopted value of e, (4.770 ±0.005) x IO_1 ° aDS - es units, with these same con- 

 stants, to evaluate d' . 



d' 2 o = {4-77ox w 10 / 1.7 176 x io 13 p = (3.0283 ±0.0010) x io -8 cm 



This value of d' 20 includes the result of the X-ray work, since the value of e 



just used is the weighted average from both oil-drop and X-ray work. We 



might have used £ = 4.768 to get a value of d' based on oil-drop work. A second 



value of d' might then be obtained from absolute X-ray measurements. The 



weighted average of these two values would be the value given, provided we 



use the data and probable errors indicated on p. 91. 



We obtain for the effective grating space of calcite at 20°C, for the first order 



spectrum, , . N R 



r d 20 = (3.0279±o.ooio) x io _8 cm. 



This value is to be substituted with the direct experimental value of V sin 6. 

 For the latter Duane, Palmer, and Yeh found 2039.9 ± l mT - volts (mean tem- 

 perature of about 20°C). Thus we have 



h= (6.559 ±0.008) X IO ~ 27 er g " sec - 

 Similarly revising Wagner's result we obtain 6.532 ±0.010, in place of 

 6.526 ±0.010. It is difficult to judge what revision is required in the values of 

 X used by Wagner ; the change is probably small. We thus have, as the two best 

 values of h, from X-ray data, 6.559±o.oo8 (or 0.009) an d 6.532±o.oio. The 

 work of Wagner has not yet been published in sufficient detail. For this reason 

 in adopting a weighted average only one-half as much weight is given to 

 Wagner. Since the two results differ by much more than the probable error 

 of either, the regular least squares probable error is used. Hence, from X-ray 



data, . ,, x o 7 



h= (6.550±o.oo9) x io~- 7 erg • sec. 



(d) Photoelectric effect. — The most accurate determination of h, from 

 photoelectric work, is by Lukirsky and Prilezaev. 1 They use a somewhat 

 different technique from that employed by Millikan, 2 and obtain a simple 

 empirical relation for the ionization current as a function of voltage. The 

 actual curve may be transposed into a linear graph, making the extrapolation 

 to zero current more certain. They also carry the readings very close to this 

 zero point. 



1 Zeit. Phys., 49, 236, 1928. 2 Phys. Rev., 7, 355, 1916. 

 Smithsonian Tables 



