J. P. Cooke on the Spectroscope. 309 
the collimator. In order to facilitate this adjustment the tele- 
Scopes are provided with caps which cover the object-glasses of 
through the observing telescope was brought into exact coinci- 
dence with the vertical wire and the position of the vernier noted. 
€ prism was now brought back to its place by turning the up- 
nine prisms of the Cambridge spectroscope measured as just de- 
scribed, and in a parallel column the same angles measured in 
the old way with the prisms at the center of the plate. It will 
limits of error of observation : 
be seen that the differences are insignificant and within the 
Measured at Measured on 
center of plate. edge of plate. 
No. 1, 90° 31'.10% . 29" 31! 19" 
No. 2, 29° 29/ 10” 29° 29 10" 
0. 3, 29° 28/ 10” 29° 28/ 10” 
No. 4, 29° 37/ oO” 29° 36! 411” —20" 
No. 5, 29° 28/30" 29° 28/ 40” +10" 
No. 6, 29° 36/ 30” 29° 36’ 10” 20" 
No. 7, 29° 28 104 29° 28/ 10” 
No. 8, 29° 29° 30" =629° 29°40" 4-10" 
No. 9, 29° 28! 40” 29° 29/ 40” 
267° 37' 50" = 267° 37’ 30” —20" 
ape a the adjustments required may appear complicated, 
ey ca 
n be made in far less time than it has taken to describe 
hod 
Sct—Szconp Senres, Vou. XL, No. 120.—Nov, 1865. 
