212 
Transactions, dec. 
TMontlily Microscopical 
L Journal, April, 1, 1869. 
III. — Two New Forms of Selenite Stages. 
By Frederick Blankley, F.E.M.S. 
Plate IX. 
{Read h&fore the Royal Microscopical Society, March 10, 1869.) 
I HAVE much pleasure in submitting to the Fellows of this Society 
two new forms -of Selenite Stages, which I hope may assist our 
researches in that beautiful and fascinating study — the study of 
polarized light. 
As some objects are affected more by one colour selenite than 
another, I found it desirable to view each object with different films, 
in order to observe under which colour the structure could be seen 
to the best advantage. 
In placing the different selenites under the object, it occurred 
to me that much time and trouble would be saved if the selenites 
could be so arranged that they might be removed without taking 
the object out of the field or focus. This led to the construction of 
THE Sliding-stage, which consists of a small brass stage 3 J in. long 
and 1^ in. wide, in the centre of which is an aperture through 
which the object is viewed. On the under part of the stage is a 
dovetail groove, into which is fitted a brass slide containing three 
or four selenites, which work freely as the investigator may desire. 
A small spring, stops the slide when the selenite is immediately 
under the aperture. 
The Compound Selenite Stage consists of a brass stage of 
similar dimensions to the one just described ; and, in addition to 
the brass slide, has a revolving diaphragm with three selenites, each 
made to rotate, and a clear aperture, so that the object may be 
viewed with a single film, if desired. 
In this stage, each selenite is much larger than those in the 
small one, and is marked in quarters, so that the colours obtained 
may be registered and turned to at any time. 
The positive axis of each selenite in the diaphragm is marked 
coincident with those in the slide. 
To increase the variety of colours and tints, rotate each selenite 
until their cleavage is at the right angle of the positive axis of those 
on the slide. 
By working each film as thus described, twenty-eight colours 
and tints will be obtained, and can be recorded for future reference. 
I think, in using this stage, even a greater number of tints can 
be seen than the number quoted by Mr. Swift, who is preparing a 
complete hst of changes that can be effected by it. 
It is only just to him to say that he has rendered me much 
assistance by his practical knowledge, and placing the whole of his 
stock of selenites at my service. 
