Anniversary Meeting. 
41 
is required in examining these objects than in selecting the 
most desirable aperture^ and focussing the condenser for that 
illumination which defines the best ; too much and too little 
light being equally bad. 
If it be wished to examine objects such as Pleurosigma 
formosum, P. quadratum, P. angulatum, and their allies, put 
No. 11 aperture in the field, rack up the condenser until the 
field is very bright, then put on No. 1 stop, rack up the con- 
denser until the stop disappears, and if the desired eflPect is 
not produced try No. 2 stop; the condenser will then require 
to be racked up still higher, and the dots will come out 
admirably. 
If it be wished to examine Navicula cuspidatum, N. rJiom- 
boides, Pleurosigma fasciola, P. macrum, or their allies, still 
use No. II aperture, and stop No. 2, which will have to be 
altered a little in position, when the checks will distinctly 
appear. 
For the Amician test use the slots instead of No. 2 stop ; 
and as regards very difficult lines, such as those of the Acus, 
the condenser must be so arranged (when focussed up till the 
field becomes exceeding bright) that a shade be thrown on the 
object from the left hand, and No. I or No. 2 stop used, so 
as to darken a little the right hand side of the field; the 
effect will be to bring out these delicate lines. The -^th and 
-pVth object-glasses I have generally found the best for this 
object with the B eye-piece; in fact, the B eye-piece is 
mostly to be preferred with high powers. 
In the foregoing remarks I have been compelled to allude 
to my own apparatus ; still, no doubt, the same effects may 
be produced by the use of condensers of different construc- 
tion, as long as the aperture is considerable. 
See Engraving for the arrangement of the microscope and 
lamp. 
MICROSCOPICAL SOCIETY. 
Anniversary Meeting. 
February \Uh, 1866. 
J. Glaisher, Esq., F.R.S., President, in the Chair. 
The minutes of the preceding meeting were read and con- 
firmed. 
Various presents were announced, and the thanks of the 
meeting returned to their respective donors. 
