300 
PROCEEDINGS OF THE SOCIETY. 
contributed most important general theorems, whence the passage of 
rays of light through systems of lenses could be determined. In the 
current number of the Society's Journal was a translation of a paper 
by the late Prof. G. Govi, in which that distinguished physicist 
endeavoured to still further simplify computations of that kind. He 
mentioned these facts because Mr. Nelson seemed rather to suppose the 
theory had not received the attention it merited, inasmuch as Heath’s 
recently published work on optics dealt with it only partially. He 
(Mr. Mayall) thought English publishers of scientific works had hitherto 
been very remiss in not supplying English students with translations of 
the best German and French works on optics. Gauss’s works were still for 
the most part unknown in England, as also were Listing’s. Mr. Adolphe 
Martin’s application of Gauss’s theories to optical instruments, and 
M. Croullebois’s development of them in connection with lenses of given 
thicknesses, ought to appear in English. There was also Yerdet’s 
£ Optique Physique,’ and many other optical works of great importance, 
which were, of course, known to professional mathematicians in England ; 
but they were hardly referred to in the textbooks in general use. 
Mr. Mayall said that since the last meeting he had received another 
notification from the authorities of the Antwerp Microscopical Exhibi- 
tion, giving further details than those which he was able to communicate 
at the last meeting of the Society. From this it appeared that the 
exhibition was to be open during August and September next, and the 
proposed mode of classification was given (see ante , p. 271.) It was clear 
the exhibition was intended to be pretty exhaustive, and if in each class 
there was only a moderate representation, the whole would be likely to 
form a very interesting collection. 
Prof. Bell said they had also received from the General Secretary 
of the International Congress on Hygiene, to be held in London in 
August next, an invitation to appoint delegates to represent the Society 
at the meetings, and thinking it very desirable that they should be 
so represented, the Council had requested the President and Dr. Dal- 
linger to undertake the duty. This congress, he might mention, was 
the seventh of a series which had been held in all the great capitals 
of Europe except Great Britain, and it was expected that the forth- 
coming gathering would be one of the most important yet held. 
The President announced that arrangements had been made to hold 
an exhibition meeting and conversazione of the Fellows of the Society 
on the evening of Thursday, April 30th. 
The following Instruments, Objects, &c., were exhibited:— 
Mr. C. Baker : — Baker’s Improved Student’s Microscope. 
Mr. J. B. Robinson ; — Photographs of LopJiopus crystallinus. 
Mr. C. Rousselet : — Hydra tuba, Medusa stage. 
Mr. T. Charters White : — Infiltrated sections of Bone and Dentine. 
New Fellows. — The following were elected Ordinary Fellows: — 
Messrs. Kay Lees, F.R.C.V.S., Alfred B. Loder, J.P., and Colonel 
Alexander Ewing. 
