GASEOUS REFRACTIVE INDICES 

 Table I 



283 



Element 



Hydrogen . 



Helium 



Neon. 



Argon 



Krypton . 



Xenon 



Fluorine . 

 Chlorine . 

 Bromine . 



Iodine < 

 Oxygen 



Sulphur 



Selenium . 

 Tellurium . 



Nitrogen . 



Phosphorus 



Arsenic 



Zinc . 

 Cadmium 



Mercury 



Refractive Index 



Refractivity 



(/A — i) IO 6 



»-i=a(i+ b -) 



•0001 



358 ( 



I + 



1) 



6-67 

 io"X : 



•00006956(1 +^n) 



10001374 . 

 •000c eSi If -"- 



•000 



•OOOI 



5584 (1 + 12-) 

 8378 (1 + £2L) 



3 6 4 6 (1 + £I4) 



1 000195 

 1 '000768 

 1001125 

 1-00192 violet\ 

 1*00205 re( i J ' 



•0002663 (1 + 5'Q7\ 

 J v X-10"' 



■°° I04S7 ( I + S) 



1*001565 

 1 002495 



X-io 1 



■00029061 ( 



I + 



77 



X-'io" 



153 



•OOI l62 (l + — Li \ 



rOOI552 



r002050 

 I-002675 



•001755 (* + |£§) 



x X-'io" 7 



\ = 00 



135-8 

 69*56 



558*4 

 837-8 

 13646 



266-3 

 1046* 



290*6 

 1162* 



1755' 



a = 3893 



138-4 



7000 



I37-4 

 567-4 



854-6 



1404* 



i95 

 768 

 1125 



2702 



11 1 1 



1565 

 2495 



297-1 



1212* 



1552- 



2050- 

 2675- 



1866- 



Em- 

 pirical 

 Ratios 



I 

 2 



8 



12 



20 



2 



8 



12 



20-! 



12 



20 



12 



? 

 ? 



Divergence of 

 experiment from 

 col. s per cent. 



K = 00 



Stan 



+ -3 

 + -4 



- i'9 



Stan 



Stan 



- r8 



Stan 



A = 5893 



dard 



- i'9 

 + 1-3 



+ r6 



+ i-5 

 dard 



- 2*3 



o 

 + 6*4 



dard 



+ 2-2 



- 4- 

 -8- 



dard 



+ 2-03 

 - 17- 



Observers. 



Scheel 



W. Burton 



Ramsay and Travers 



W. Burton 



C. and M. Cuthbertson 



Cuthbertsonand Prideaux 

 Mascart 



>> 

 Hurion 



Mascart 



Cuthbertsonand Metcalfe 



11 11 



ii 11 



Scheel 



Cuthbertsonand Metcalfe 



The broad facts of this table are at the same time very 

 simple and very puzzling. In no less than five different groups 

 of the elements we find that at least in one case and sometimes 

 in more than one the refractivities are in the ratio of integers 

 so simple as 1, 2, S, 12, and 20, of which the last three can be 

 reduced to 2, 3, and 5. 



If we except the case of mercury, or challenge its admission 

 to the group which contains zinc and cadmium, the rule is that 

 in each group the refractivity increases as the atomic weight 

 increases, though not regularly. But for the case of helium 

 it could be said that the refractivity increases much faster than 

 the atomic weight, i.e. in the ratios of 1 to 10, while the 

 atomic weight increases in the ratio of 2 to 13 ; but between 



