108 
Brown iNGj on the Application of 
2nd. By giving a spectrum of an uniform length any 
description of micrometer may be used for taking the mea- 
surements of the position of the bands. 
As the microscope armed with this auxiliary apparatus will 
probably before long be used for obtaining the spectra of the 
absorption-bands of blood in criminal cases, the importance 
of being able to reduce observations to actual measurement 
can scarcely be over-estimated. 
Fig. 1. 
In Fig. 1 a prism is placed at which is enclosed in a box, 
so as to give a black field by excluding extraneous light. 
The ray of light, after passing between the knife-edges at k, 
are rendered parallel by means of the lens at l. Then pass- 
ing through the prism and condenser (c), they reach the 
objective of the microscope. The light is placed at w. If 
it is proposed to examine a liquid it can be placed in a small 
tube (t), closed at one end. A transparent preparation may 
be placed on the stage s at o. 
By the addition of a small telescope instead of a condenser, 
this contrivance can be applied to a microscope in place of 
the eye-piece. It can then be used for the examination of 
opaque objects. 
For simplicity and economy this arrangement will proba- 
bly be preferred to any of the other contrivances which have 
been proposed, and to which I shall presently refer. 
At the last monthly meeting Mr. Wenham communicated 
a very valuable and suggestive paper by W. Huggins, Esq., 
F.R.S., on Spectrum Analysis applied to the Microscope.^-* 
Mr. Huggins had in view principally the best means of 
obtaining the spectra of the contents of various kinds of cells, 
believing that experiments in this direction would be of great 
value to physiologists. 
The apparatus Mr. Huggins has used for the purpose con- 
sists of a star spectroscope, which I made for him ; of which 
the coUimating tube was inserted in the body of the micro- 
scope instead of an eye-piece. With this contrivance he has 
