PROCEEDINGS OF SOCIETIES. 291 
Sorby’s diagrams, but he did not perceive what progress had 
really been made in the instrument, and he thought that the 
matter stood just where it was left by Mr. Sorby in his paper in 
the ‘ Quarterly Journal.’ How far he would be able to work out 
a direct-vision prism remained to be seen; but what was required 
was some actual result. 
Mr. Brownine stated he had received four letters from Mr. 
Sorby, in which that gentleman said that a direct-vision prism 
with which he had been supplied gave him all he required. With 
reference to what Mr. Beck had said, he would remark that if they 
tried to examine a spot of blood on the microscope with an instru- 
ment. which could only be used for transparent objects, a success- 
ful result would, of course, not be likely to be obtained. 
Mr. Brooxr.—I do not understand by what means Mr. Sorby’s 
original apparatus can be applied to opaque objects. 
Mr. Becx.—That is precisely the tendency of the remark I 
made. 
Mr. Brownine.—Mr. Sorby is now engaged with the direct- 
vision prism examining opaque objects. 
Mr. Brooxe.—But, as far as 1 understand, the production of 
spectra from that spot of blood is a result obtained, and one 
which could not have been obtained from Mr. Sorby’s original 
apparatus. I should like to ask Mr. Browning if as good defini- 
tion could be obtained by the compound prism as by an ordinary 
train of prisms placed in the usual way. 
Mr. Brownine.—Where low powers are used, and the spectra 
are small, I believe equally so. I cannot distinguish between 
them. This instrument, which contains only a simple prism, 
placed at the angle of deviation in the ordinary way, does not give 
superior results. 
Mr, Brooxn.—I was only judging from the spectroscopes which 
I saw about three years ago in the Exhibition, and which were 
not so good in definition as the ordinary instrument. 
Mr. Brownine.—That arose from using prisms with too obtuse 
angles. Hoffman uses prisms with angles of 90°. Nearly all the 
prisms are made of flint-glass, with masses of veins in it. Dr. 
Miller, who was in the room just now, gave me one of Hoffman’s 
to adapt to his microscope, and we found it so veiny that we could 
not use it for the purpose at all. The lines were not sharp enough. 
Mr. Slack has seen the action of Mr. Gassiot’s prism. It is a 
direct-vision prism, such as is shown there, for getting the spectra 
of metals. Mr. Huggins has used it, but he had no fault to find 
with it, and, indeed, liked its performance very much. 
The CuarrMAn said—The paper Mr. Browning has read was 
promised last month. I am now very glad that I did not press for 
it. The letter quoted by Mr. Beck, in which Mr. Sorby states 
that direct-vision prisms do not perform satisfactorily, was written 
on the 22nd of last month; the letters Mr. Browning has just 
aliuded to have been written by Mr. Sorby this month, one so 
late as the day before yesterday ; in them he states that such im- 
VOL. V.—NEW SER. x 
