L. M. Rutherfurds Spectroscope. , = 
Careful and repeated measures give for the index of refraction 
of the soda line with the prism first filled from the bottom, 
1:62876, and with the ninth prism, filled with the fluid near the 
upper portion of the jar, 1°62137. 
In order to obtain fine definition, it is necessary that the prisms 
should be placed at the angle of least deviation for the ray under 
observation. To make the adjustment with several prisms, or to 
change it when made, is so laborious and troublesome a task as 
almost to amount to a prohibition of the use of a powerful bat- 
tery for practical and extended investigations. To remedy this 
evil Thave devised and executed a mode by which I 1. the 
“J4stment of all the prisms by one motion of a milled 
An inspection of the sooomipanying Fig. 1, which represents the 
