The Presidenfs Address. 
21 
Twenty new members have been elected during the past 
session ; and our present numerical strength is 349, against 
353 at the last anniversary. As, however, several names 
have been removed from our list, comprising those who 
have for several years ceased to manifest any interest in our 
proceedings, or to contribute" to our funds, 1 am not inclined 
to think that our effective force is in any degree diminished 
or impaired. 
The available powers of the microscope have recently been 
largely augmented by the successful construction of an ob- 
jective of 3ioth-inch focu^ by Messrs. Powell and Lealand. 
These able mechanicians have long held the foremost position 
in the construction of very high magnifying powers, having 
first produced a -pVth in the year 1840, and a ^i^th in 1860. 
It must, however, be borne in mind that the priority of con- 
struction of an effective -^-^th^ objective is due to Mr. Wenham, 
to whom the microscope has been so largely indebted for its 
developments ; this excellent glass was completed by him in 
the summer of 1856. It is constructed on a principle differ- 
ing from that usually adopted in the construction of deep ob- 
jectives, in having a single front lens. The advantages of this 
mode of construction appear to me to be considerable, and to 
merit the careful attention of opticians. 
This triumph of optical skill has been constructed for Dr. 
Beale, and as I have not myself had the opportunity of more 
than a casual inspection of it, it may not be inappropriate to 
quote from the ^ Proceedings of the Royal Society,^ vol. xiv, 
p. 35, Dr. Beale's own account of its performance : — The 
--Vth is even better than the -^-^ih, which is now made instead 
of the -^-^th.. Plenty of light for illuminating the objects to 
be examined is obtained by the use of a .condenser provided 
with a thin cap, having an opening not more than 3^^th-inch 
diameter. The preparation may be covered with the thinnest 
glass made by Messrs. Chance, or with mica ; and there is 
plenty of room for focusing to the lower surface of thin 
specimens, which can alone be examined by high powers 
transparent objects. 
" I beg to draw attention to these very high powers, at this 
time more particularly, because the facts recently urged in 
favour of the doctrine of spontaneous generation, lately re- 
vived, may be studied with great advantage. Not only are 
particles too small to be discovered by a -Vth well seen by 
a ir'-^th or a xo^h, but particles too transparent to be observed 
by the -^-jth.^ are distinctly demonstrated by the ^V^h. I feel 
sure that further careful study, by the aid of these high powers, 
of the development and increase of some of the lowest 
