290 PROCEEDINGS OF SOCIETIES. 
difference between the uses of the two instraments—Mr. Sorby’s 
original instrument represents the application of the microscope 
to the spectroscope; on the other hand, fig. 7 is the application 
of the spectroscope to the microscope. In that case we produce a 
spectrum of very small size, and magnify it up again. We are 
necessarily limited to low powers; but, according to my limited 
experience with the instrument represented by fig. 7, the higher 
the power the better the result. 
Mr. Brownrne.—That is so. 
Mr. Wenuam.—I should like to ask Mr. Browning the width 
of the jaws under the slit. As far as I have observed, it has 
always seemed desirable to get rather a wide slit, because in 
having it close to the prism we get it narrow, and the loss of light 
from dust and other irregularities on the edges of the jaws are 
detrimental to the effect. Mr. Wenham then asked Mr. Browning 
if he had observed the actual width of the slit. 
Mr. Brownrne said he had not. He thought it must be some- 
where between 7,35 and 7,5 of an inch wide. He might add 
that Mr. Sorby was quite of Mr. Wenham’s opinion, that the 
spectroscope should be applied to the eye-piece of the microscope. 
Mr. WenHAM said that it showed indications which could not 
be seen in the ordinary way. With the other instrument it was 
difficult to analyse a fluid of any thickness ; but if an apparatus 
could be produced on the opposite plan, they would be able to 
examine the cells of the blood or of chlorophyll. 
Mr. Snack referred to some experiments which he had made 
with Mr. Browning’s instrument, and said that the prism found 
best for observation of the bands might be inapplicable to many 
purposes for which microscopists would like to use the apparatus. 
He felt sure that Mr. Browning’s arrangement would prove a 
valuable one; but the question of expense was one of some 
importance. Mr. Slack added, as soon as Mr. Browning had given 
him the opportunity of trying the prisms made for Mr. Gassiot’s 
electrical experiments, it had occurred to him that there was the 
very thing that was wanted, and the application of it that had 
been made seemed to warrant that idea. 
The Cuarrman asked Mr. Browning to state the price at which 
the spectroscope could be applied to the microscope, and whether 
it was equally available for transparent and opaque objects. 
Mr. Browntne said that Mr. Sorby’s object and his own had 
always been to produce the most perfect kind of instrument at 
the lowest possible price, and he felt confident that when the 
instrument was made as perfect as it could be made its cost 
would not exceed £4 or £5. 
Mr. Beck said it appeared to him that no definite result had 
been produced, and that Mr. Sorby had not yet obtained a prism 
which gave what was actually required. The one he tried was not 
convenient in use, and the other did not give sufficient dispersion. 
He had examined a spot of blood with the former, but without 
obtaining a satisfactory result. He had seen nothing except Mr. 
