322 
PROCEEDINGS OF SOCIETIES. 
Mr. Charles Brooke inquired if any time was stated as being 
required for the deposition of the germs of the monads ? 
Mr. Stewart said that it appeared from the paper that after the 
first introduction of the powder four and a half hours were allowed for 
the subsidence of the coarser particles, and then it was left for twenty- 
four hours ; after this the covers were removed and the vessels left 
for four days before their contents were examined. 
The President said that his attention had been drawn to analogous 
phenomena, and he had found that although the rate at which 
particles of a substance subsided is in proportion to their size, yet 
the relative positions of the particles at the time their subsidence took 
place must also be taken into consideration. 
Dr. Lawson inquired to what temperature the dried-up portion of 
cod's head had been submitted ? 
Mr. Stewart said it was 150° Fahr., a temperature which it had 
been previously proved was sufficient to kill the adult forms of the 
monads. He thought it quite probable upon the face of it, that the 
germs derived from the larger forms would be in themselves larger 
than those of the small forms, and therefore it might be inferred that 
they would probably subside first. 
Dr. Lawson remembered that in cases where Botifera had been 
subjected to an exceedingly high temperature, they had survived in 
those instances in which the heat had been gradually applied. 
The President said that the temperature which had been men- 
tioned was that which coagulates albumen, and might thus destroy 
life for which albumen is necessary, but not in those cases in which it 
is unnecessary for life. 
Mr. Stewart did not think it followed necessarily that the 
creatures themselves had been exposed to this temperature, as they 
might have been protected by some surrounding covering. 
A paper by Mr. Wenham, " On the Measurement of the Angle of 
Aperture of Object-glasses," was read by Mr. J. E. Ingpen, and illus- 
trated by drawings on the black-board enlarged from the diagrams 
accompanying the paper. It will be found at p. 285. 
A vote of thanks to Mr. Wenham was unanimously passed. 
The President said that his attention had lately been drawn a 
good deal to this subject, and he had found that in many cases the 
working aperture was much less than the aperture which had been 
stated as being that of the lens. He then proceeded to show, by means 
of diagrams drawn upon the board, a method which he had employed 
for ascertaining the angles at which rays could be sent upon an object, 
so that it might remain dark upon a bright background, the light 
being reflected upon it by means of a prism having angles of 65°, 
60°, and 65°. 
Mr. Charles Brooke suggested another means of throwing a 
parallel pencil of light upon the object, by employing a tube having a 
concave lens at one end and a convex lens at the other. 
The President recognized the merit of this plan, but suggested that 
it was open to the objection of not being so readily illuminated by 
means of the ordinary mirror. 
