320 Transactions of the Royal Microscopical Society, 
IV . — Improvements in the Micro-spectroscope. 
By F. H. Ward, M.R.C.S., F.R.M.S. 
(^Read before the Eoyal Microscopical Society, December 13, 1878.) 
Plate XYII. 
Early in tliis year we were reminded by Mr, Crisp * that one 
of the objects of this Society was the promotion and diffusion of 
improvements in the optical and mechanical construction of the 
microscope, and as during the last twelve months I have been 
making some experiments with a view to modifications of the 
micro -spectroscope, and have just received from the maker an 
instrument which differs in several particulars from the usual form, 
I have ventured to bring it before the Society, and after pointing 
out the features in it which I believe to be new, shall leave it in 
your hands to decide whether it is an improvement or not. 
One of the first things which struck me as being an imperfec- 
tion in the ordinary instrument was the slit, and the facility with 
which its jaws collect dust, thus causing those objectionable black 
lines across the spectrum, and though when the spectroscope is to 
be used in conjunction with the microscope the slit is much more 
protected from dust than in a table spectroscope, yet, neverthe- 
less, from its internal position it is more difficult to get at, and 
sometimes little particles remain after several attempts to remove 
them. I cannot claim to have done much work myself in this 
branch, but I am told that with an instrument in constant use, the 
slit is liable to get out of order, and requires adjustment to maintain 
the perfect parallelism of the jaws and the integrity of their opposed 
edges. 
As soon as I began to make inquiries on the matter, I found I 
was by no means the first who had recognized these difficulties, and 
that during the last twelve years others had been considering what 
could be employed as a substitute for the slit. Returning one 
night from one of our meetings, it suddenly occurred to me that if 
a rectangular glass prism was taken and the apex of the right angle 
carefully ground off and the resulting face polished, it would 
transmit a narrow pencil of light, which would work admirably in 
spectroscopic examinations, any light falling upon the sides of the 
DESCRIPTION OF PLATE. 
Fig. 1. — New micro-spectroscope. 
„ 2. — Plan of internal platform, showing prism fitting, with three prisms in situ^ 
comparison prism with slot, &c. 
„ 3. — Tube carrier for comparison stage. 
* ‘ Journal of the Royal Microscopical Society,’ vol. i. p. 121. 
