365 
PROCEEDINGS OF THE SOCIETY. 
MEETING 
Held on the 15th of April, 1896, at 20 Hanover Square, W., 
the President (A. D. Michael, Esq., F.L.S.) in the Chair. 
The Minutes of the Meeting of 18th March, 1896, were read and 
confirmed, and were signed by the President. 
The List of Donations (exclusive of exchanges and reprints) received 
since the last meeting was submitted, and the thanks of the Society 
given to the Donors : — 
From 
E. Pulsford, The Wonders of the Microscope. (16mo, London, 
1896) The Author. 
A Stereoscopic Photomicrograph . . . . Dr. W. C. Borden. 
The President said that this photograph had been taken in a 
rather different way from others which had been exhibited on former 
occasions. In this instance the difference between the pictures was 
obtained by tilting the object slightly from opposite sides. There was 
some little doubt as to whether there was a true stereoscopic effect pro- 
duced, but the photograph would be passed round for the Fellows present 
to examine. 
Mr. E. M. Nelson exhibited and gave the following description of a 
new form of doublet bull’s-eye condenser: — During an investigation of 
the spherical aberration in doublets an examination was made of the cele- 
brated Herschel’s doublets of “no aberration.”* Calculating the path of the 
was revealed ; the analysis showing that under the given conditions it 
was not possible to construct a doublet free from aberration. 
Further, an error in the focus of the doublet was found, and it was 
also seen that the aberration was not a minimum. 
These doublets have been quoted in many books both on the Micro- 
scope and on optics, including works by writers of high mathematical 
attainments, consequently they have gained much popularity, which is 
to be regretted, because an erroneous view of the fundamental principles 
of aplanatism is thereby propagated. 
In this condenser, which was made by Baker, the aberration is a 
* Ency. Metrop., Art. ‘ Light,’ p. 391, pi. iii. fig. 55. 
2 o 
1896 
