72 
The Presidenfs Address. 
This instrument^ so fully described by Mr. Williams, is in 
striking contrast with the small but effective instrument just 
noticed; it is, however, in all respects a remarkable pro- 
duction, whether considered with regard to the many in- 
genious contrivances, or the excellence of the workmanship 
shown in its construction. 
3. For the effective use of the microscope, improved 
methods of illumination have been proved to be of not less 
importance than improved objectives. On this subject we 
have been favoured with a communication by the Rev. J. B. 
Reade. On a nev/ Hemispherical Condenser for the Micro- 
scope, and its use in illustrating an important principle in 
Microscopic Illumination.'' (Read, 8th May, 1861. ^Tr. 
Mic. Soc. Lond.,' n. s., vol. ix, p. 59). 
^' The principle sought to be carried out is to throw the axis 
of the pencil of illuminating rays in a direction at right 
angles to the line to be resolved." The author shows how, 
by the use of a simple lens, and a few diaphragms with 
apertures at their circumference, two or more illuminating 
pencils may be thrown at the same time upon an object 
having two or more sets of lines, and the direction of the axis 
of the pencil be determined by the position of the apertures 
on the margin of the diaphragm. The arrangement is simple, 
cheap, and easy of adjustment; its efficiency was placed 
beyond doubt by the most conclusive of all proofs, actual 
demonstration. 
4. " On a Portable Revolving Table,'' by J. Burton, Esq. 
(Read, 9th October, 1861. ' Tr. Mic. Soc. Lond.,' n. s., 
vol. x, p. 9). 
This falls under the head of " arrangements for affording 
increased facilities for the use of the microscope." It is a 
simple and ingenious contrivance for enabling an exhibitor to 
submit an object to several persons seated at the same table 
with the least possible disturbance. The table was exhibited 
at the meeting, and woodcuts of it are published in ^The 
Transactions.' The contrivance appears to be well calculated 
to accomplish the design. 
B. On Crystallography. — This paper well illustrates the in- 
fluence of improvements in the construction of the microscope. 
It is " On the Microscopic Characters of the Crystals of 
Arsenious Acid," by William A. Guy, M.B., Cantab., Profes- 
sor of Forensic Medicine, King's College, London. (Read, 
8th May, 1861. ' Tr. Mic. Soc. Lond.,' n. s., vol. ix, p. 50). 
We must all admire the skill manifested in explaining the 
phases of the octohedron, to which form most, if not all, of 
