771 Prof. JEL Rubens and Mr. H. Hollnaoel on 



The two other series gave the values 62'2 and 70*5 fi and 

 62*1 and 70*4 fx for X x and \ 2 respectively ; furthermore, 



the constants y l% y 2 , and ~ coincided practically with those 

 obtained from this plot, t* 1 



Re&tstralilen of Potassium Bromide. 

 Of the three curves which were obtained, two are drawn 

 in fig. 5 ; /3 was observed under most favourable circum- 

 stances. Tables of the maxima and minima follow : — 

 Series a. Series /3. 



Maxima. 



Minima. 



a 



b 



c 



d 



e 



/ 



9 



h 



104 

 960 



88-0 

 80-0 



61-9 



53-8 

 45 9 



a! 



V 



c' 



d' 



e' 



/ 



9' 



h' 



999 

 917 



83-9 



58-0 

 50-5 

 42-5 



Maxima. 



Minima. 



a 



b 



c 



d 



e 



/ 



9 



h 



103 6 



95-7 



87-9 

 80-1 



61-0 



53-3 

 4.V4 



a! 



V 



c' 



d' 



c' 



./" 



g ' 



h' 



997 

 91-6 

 83-8 



57-7 

 499 

 41-8 j 



Homologous points are a and h as well as a' and li . 

 Hence n = 14 and A = 57*8 or 58*1 respectively:— 



Series a. 

 a-h = 58*1 

 d-h'= 57*5 



Series @. 

 a-h = 58-2 

 a!-h'= 57-J) 



A = 57*8 



A = 58-1 



Ai- 5 ^. 20-91 = 86-3 fi. 



Xi= 86'S p. 

 a 2 = 76*0 ^ 



Ao = A,] — ; = i O ll. 



±0 r 





7l = 0-18. 72= 0-158. 



^=074. 

 Pi 



For the third series \ 1 = 86'4/u, and X 2 = 75'5ya were 

 obtained. A comparison of these results with the conclusions 

 arrived at by E. Aschkinass regarding the maximum of re- 

 flexion of potassium bromide, as deduced from the reflectivity 

 of this salt for Reststrahlen of rock-salt and sylvine, i. e. 

 that it probably lay between 60 and 70 fi, proves the latter 

 estimate to be considerably too low. 



