130 L. M. Rutherfurd’s Spectroscope. 
graphic purposes, also warmed and both surfaces to be in cow 
tact dusted with a fine camel’s hair brush, was placed in position 
upon the prism, a hot and fluid mixture of glue and : 
was then applied with a fine brush around the edges of the 
glass, whereupon a uniform and verv thin film of the cement 
that my description is needlessly particular, but I have mentioned 
nothing which experience has not shewn to be necessary tol 
permanence or performance of the prism. ee 
soon discovered that, after I had made a good prism, tts per 
formance would be uncertain, and I finally traced the difficulty 
to a want of equal density in the bisulphid of carbon, and: 
peculiarity. I have observed not only in the fluid of commer 
upper part, and bisecting the soda line with a spider’s web! 
eye-piece, all parts of the instrament being clamped, then ¢ 
ing all but the lower portion of the prism, it will be found 
the soda line has been carried to a notable extent toward 
violet end of the spectrum. 
_ This want of homogeneity in the bisulphid of carbon is entl 
different from the disturbance of density by thermal vara 
It is a permanent feature of some specimens of the fluid, 
equable temperature. I have one such prism, filled nearly § 
trata is quite a measurable quantity. My mode of over 
e bisulp id 
~— Stopper at the top. After remaining undisturoe® , 5 
s the liquid arranges itself according to its density, 
fill the prisms from the faucet, being careful 
e 
