404 



'.Dr. L. Silberstein on the 





X. 



^calc. 



^obs. 



V- 



Cd 313 



0-3133 x 



2-5247 



2-5254 



4- -0003 



„ 325 



03251 4 



2-5 J 32 



2-5130 



4- -0002 



„ 340 



0-3403.- 



2-5003 



2-5008 



-0005 



„ 346 



0-3446 3 



2-4955 



2-4951 



4--0004 



„ 361 



0-3610- 



2-4856 



2-4853 



+•0003 



„ 467 



0-46/8, 



2-4401 



2-4410 



-•0009 



„ 480 



0-4799, 



2-4371 



2-4370 



+•0001 



„ 508 



0-5085, 



2-4306 



2-4308 



-•0002 



Na589 



0-5890., 



2-4171 



2-4172 



-•0001 



Cd643 



0-6438, 



2-4107 



2-4109 



-0002 



H a 656 



0-6563 



2-4095 



| 2-4100 (Walter, 16° C.) 

 1 2-4103 (Wulfing) 



-•0006 



Li 670 



0-6708 2 



2-4081 



2-4084 5 (Schrauf) 



-0003, 



A 760 



0-7604 



2-4016 



1 2-4024 5 (Walter, 16° C.) 

 1 2-4024 (Wiilfing) 



-•0008 



With the only exception of Cd 467 (A/a =- -0009), the 

 coincidence is almost perfect, and the deviations are, from 

 •313 to *643 micr.j pretty irregular. Even the three values 

 obtained by other observers and, of course, with another 

 sample of the crystal, although showing a tendency to 

 increasing negative A/a, are too small to point to a systematic 

 deviation of experiment from theory. 



Future, more precise, measurements of the refractive 

 index of diamond may reveal some discrepancies. But for 

 the present we are justified in asserting that the one-term 

 formula 



/- 2 -i = ,t^: (9) 



llQ—U 



represents the observations with all desirable accuracy. 

 By (8) we have for the atomic constant of carbon denoted 



previously {loc. 

 meaning is 



cit. p. 527) by k 0y and whose immediate 



ko = 



1-008 



37T 



m 



e c 



Nin- 



th e value 



7 1M 



A ' 0= 3¥ 



(10) 



(H) 



It will be remembered that if e' be the charge of an electron 

 proper, the numerical value of k is 



e=l-83. 10 10 cm.gr.- 1 . 



