SHORT REPORTS FROM THE CHEMICAL LABORATORY 
; OF TRINITY. COLLEGE, DUBLIN. 
BY 
J. EMERSON REYNOLDS, m.p., 
Professor of Chemistry, University of Dublin. 
No. LV. 
On a New Form of Measuring Apparatus for a Laboratory 
Spectroscope. 
[ Read February 19th, 1877.] 
THE measuring apparatus for a laboratory spectroscope which 
I have been asked to describe, was fitted about a year ago to an 
instrument in common use in the College Laboratory, and has 
afforded very satisfactory results. My chief aim in planning the 
arrangement, was to facilitate the measurement and identification 
of spectral lines and the mapping of spectra under circumstances 
admitting of little general illumination. 
The spectroscope to which the apparatus is fitted has two fixed 
flint glass prisms, the refracting angle of each being 60°. This 
instrument is shown in the annexed engraving. When in use 
the prisms are covered by a brass cap provided with openings for 
the collimating and observing telescopes. The movable arm 
D that supports the observing telescope also carries a vernier 
which is moved with the telescope over a graduated arc, and in 
this usual way the relative positions of the several lines of a given 
spectrum can be determined. The angular distance traversed in 
passing from the extreme red to extreme violet is necessarily 
small owing to the low dispersive power of the instrument ; but 
this, I need scarcely say, is an advantage rather than the reverse 
in a spectroscope which is commonly employed as an aid in 
ordinary qualitative analysis. 
For Report No. I., “On Glucinum; its Atomic Weight and Specific Heat,” see Philo- 
sophical Magazine [5], vol. iii., p. 88; for No. II., ‘On a New Mineral Borate,” and 
for No. IIL, “On an Analysis of Lievrite, by Mr. Early’s Method,” see Phil. Mag. [5], 
vol, iii., pp. 284 and 287. 
