196 Dr. J. E. Rydberg on a certain Asymmetry 



Always supposing, as in the preceding, that this curve also 

 passes through C, we see on fig. 1 where C0 4 is a diameter 

 of* the true focal circle, that the angle between CO and CO x 



is 



= 8 = 



IT 



6. 



We have then 



18261" 



tan £ = cot e 



P 



The determination of the radius of curvature has 

 p = 6434±l Hiillim. According to the statement engraved 

 on the grating, « = 00001 inch =0*00254 millim. From 

 this we obtain S = 24 / 47 // and the arc OO^p tan 8 = 18261 co 

 = 46'4 millim. The difference between the diameters CO 

 and COi amounts to 0*17 millim. 



IV. Though there could be no doubt as to the obliquity of 

 the grating, it was possible that we had to do with some 

 accidental anomaly peculiar to our special grating. For that 

 reason it was of great interest for me to find an opportunity to 

 examine another grating of the same kind, and this has been 

 made possible through the kindness of Dr. A. E. Andersson 

 at Kristianstad, who has been good enough to place at my 

 disposal a concave Rowland grating of exactly the same kind 

 as the preceding. 



The measurements, which have been executed in the same 

 order as before, follow here : — 



i 



Spectral 

 line. 



Wave- 

 length. 

 lOhiX. 



a v 



a 2 . 



iK+^) 



Obse 

 d r 



rved. 

 d 2 . 



Calcu- 

 lated. 



d. 



I. h... 



1X5165 



1303 



155-6 



143-0 



-12-3 



+ 13-0 



11-6 



I. D... 



1x5893 



129-2 



158-5 



143-9 



-13 4 



4-15-9 



13-2 



11. & 4 ... 



2x5165 



118-3 



164 6 



141-5 



-24 3 



+220 



23-2 



II. D... 



2x5893 



115-5 



168-7 



142-1 



-27-1 



4-26-1 



26-4 



III.& 4 ... 



3x5165 



1086 



177-4 



1430 



-34-0 



4-34-8 



34-8 



IILD... 



3x5893 



104-2 



181-1 



142-7 



-38-4 



4-38-5 



39-7 



IV. ft 4 ... 



4x5165 



95-5 



189-6 



142-5 



-47-1 



4-47-0 



46-4 



IV. D... 



4x5893 



89-7 



195-3 



142-5 



-529 



4-52-7 



52-9 



Mean 1426 



The probable errors of the values of a are a little greater 

 than in the preceding case, and amount in maximum to 0*5 

 millim. Moreover the adjustments of the grating are not of 

 quite the same exactitude, owing to the limited time I had at 

 my disposal for making these determinations. Hence, there 

 is nothing astonishing in the fact that the mean, 142*6, of 

 the values of a differs a little more from the normal value, 





