Microscopical Society of Victoria. 
99 
to mount tiie diatoms on tlie cover whenever they require a high 
power to resolve them; and if this bo done, and if covers are used 
which have been all gauged to a particular thickness, the adjust¬ 
ment of the screw-collar of the objective will be the same for 
every object so mounted, and the trouble of making this adjust¬ 
ment for each slide will be obviated. 
If Folycistina or Foraminifera are to be mounted, a thicker 
layer of gum should be placed on the slide than for diatoms, as 
these objects, from their peculiar forms, have usually a very small 
part of their surface in contact with the slide. 
It is of course open to question whether these slides are worth 
the time bestowed upon them, but as it is comparatively rare to 
obtain gatherings consisting of one species and free from foreign 
matters, it becomes necessary to select the diatoms, and when this 
has to be done it is not much more trouble to arrange them 
symmetrically. As the pleasure which an artistic eye finds in 
orderly arrangement may be obtained at so small an additional 
expense of time and trouble, I think we may consider this 
branch of microscopic art as quite legitimate, provided, of course, 
that scientific value is not sacrificed to mere prettiness. For 
instance, when a pure gathering containing one predominant 
species can be obtained, it should be mounted in the mass, as there 
are almost certain to be variations of form, marking, or develop¬ 
ment, some of which would probably be passed over if a few 
specimens were selected and the rest thrown aside. 
For some months past I have used the gum process with all 
balsam-mounted diatoms, even when they are not arranged 
symmetrically, for the sake of the security it affords against the 
valves being displaced by slight pressure on the cover-glass, or by 
the slide being kept in other than a horizontal position, also for 
the advantage of being able to mount the valves in different 
positions, so often necessary in order to get an exact idea of their 
true form. 
I make use of the binocular microscope with a 1-inch objective 
for work of this kind, and I do not think a much lower power 
would be effective; indeed, for small diatoms, a £-inch would be 
preferable, provided that it had sufficient working distance to 
permit a hair or needle to be moved freely under it. 
