the Spectroscope to the Microscope. 
Ill 
bination of the direct- vision prisms invented by A. Herschel, 
Esq._, B.A, The line r r' shows the path of a ray of light 
Fig. 5. Fig. 6. 
through the prisms^ and it would be seen that the emergent 
ray r' is parallel and coincident with the incident ray r. 
About a month since, I adapted a Hoffmanns spectroscope 
to Dr. Miller^s microscope, making it occupy the place of the 
eye- piece. The performance was not at all satisfactory, and 
Dr. Miller finds the arrangement which I first described, 
when applied to the eye-piece in this way, gave much the best 
results. 
I had recently made a spectroscope for the examination of 
the spectra of the stratifications in electrical discharges for 
J. P. Gassiot, Esq., F.R.S. This instrument contained a 
compound direct- vision prism, of the form represented by 
p p p. Fig. 6. Having submitted this prism to Mr. Sorby, 
he at once gave it the preference, on the score of compact- 
ness. 
Any number of these prisms may be used, according to 
the amount of dispersion required. They are mounted in a 
similar way to a NicoFs drism, and are applied directly over 
the eye-piece of the microscope. 
The slit s s, which is used to show the lines in the spec- 
trum, is placed in the focus of the first glass (r) if a negative, 
or below the second glass if a positive, eye-piece be employed. 
One edge of this slit is movable. In using it the slit is 
first opened wide, so that a clear view of the object is ob- 
