the Spectroscope to the Microscope. 109 
succeeded in obtaining a spectrum showing the absorption- 
bands from a mere fragment of a single blood-disc^ when 
mounted transparent. 
In Fig. 2, K represents the knife-edges_, c the tube contain- 
ing the collimating lens^ p p the prisms^ t the telescope,, and 
M the micrometer; the object is placed on the stage s at o, 
and can be illuminated from below by the mirror if trans- 
parent, or, if opaque, from above, by any kind of condenser. 
Mr. Huggins also suggested that the apparatus could be 
used to examine opaque objects, but the great drawback to its 
extended use is that it is rather inconvenient and expensive. 
Other investigations have, unfortunately, prevented Mr. 
Huggins from pursuing this subject further himself at pre- 
sent, but it is greatly to be hoped that he will shortly find time 
to devote some attention to it, as the immense experience 
that he has had in all kinds of spectrum observations, and 
the important discoveries which he has made in respect to 
the spectra of the stars and nebulae would lead us to hope 
that he would have a better prospect of success in pursuing 
these investigations than an observer with less experience. 
I shall now describe the most recent contrivances Mr. 
Sorby has devised and adopted, and which I have had the 
honour of working out with him. First, then, with regard to 
the plan of mounting the spectroscopic apparatus below the 
stage of the microscope, Mr. Sorby suggested that a prism 
might probably be made of dense flint glass, of such a form 
that it could be used in two difterent positions, and that in 
one of these positions it should give twice the dispersion that 
it would when placed in the other position ; but that in 
Fig. 2. 
