254 Mr. M. Ponton's further Researches regarding 



Nos. Logs. 



p = 1-333333' 01249387 



a m 1-308333' 0*1167184 



t = 1-247222' 0-0959439 



v = 1-225000' 0-0881361 



X = 1-119444' 00490025 



$=1-082407' 00343906 



The values of the normal wave-lengths thence arising are — 



Nos. Logs. 



B = 1-000000 0-0000000 



C = 0'953291 1-9792255 



D = 0-855626 1-932284] 



E = 0-764331 1-8832816 



F = 0-706140 1-8488910 



G = 0-623944 1-7951455 



H = 0-573248 1-7583429 



Fraunhofer's two sets of observed values referred to B as 

 unity are — 



C D E F G II 



I. 0-954349 0-855962 0764660 0704053 0-623770 0-571035 



II. 0-953168 0-855962 0765447 0706021 0624557 0-576151 



-1181 +787 + 1968 +787 +5116 



The differences between the calculated and the observed values 

 are — 



C 2nd ob. D E 1st ol). F 2nd ob. G 1st ob. H mean. 



+0-000123 +0000030 -0000329 +0-000119 +0000174 -0000345 



These latter differences are greatly less than those between 

 the two sets of observations, and are so trifling as to be of no 

 account. 



Among the observations furnished by Dr. Gladstone are the 

 following, on oil of cassia at temp. 13° C. Angle of prism 

 30° 35' 20":— 



Deviations, 



A 18° 58' 50", B 19° 11' 10", C 19° 18' 30", D19°37', E 20° 6' 10", 

 F 20° 34' 30", G 21° 36' 40". 



Dr. Gladstone affirms that, owing to an absorptive action ex- 

 erted by this medium on the violet end of the spectrum, the line 

 II is imperceptible. The following arc the corresponding indices 

 of refraction : — 



B 1-595416, C 1-599083, D 1-608243, E 1-623057, F 1-636980, G 1-667829. 



