258 THE AMERICAN MONTHLY [Sep 
holders are fixed colour screens, which are guaranteed to 
be of exactly the correct absorption, and are adjusted by 
an improved form of Sir W. De W. Abney’s colour sen- 
sitometer. 
Three negatives of the same subject are taken, each 
with its appropriate colour filter. One print is taken 
from each of these negatives, and then stained by means 
of special solutions which are supplied. The three prints 
are then bound together in superposition to form a fin- 
ished picture, and the result, if care has been exercised, 
is very fine. | 
Those who are in the habit of lecturing on microscopi- 
cal subjects, or who have hesitated to do so because they 
cannot sufficiently reproduce the natural appearance of 
objects, should make a trial of this process, and a very 
little practice with it will cause them to be gratified with 
the results. 
To View MuLTIPLIED IMAGEs-in the facets of the cornea 
of a beetle’s eye is quite simple. An easy method of doing 
it is to place on the mirror a small cross cut out of black 
or brown paper, about 3” long; illuminate in the usual 
way and focus the facets with 3’ objective. Then gently 
rack the objective upwards from the object, at the same 
time moving the paper cross on the mirror, very slightly, 
with a needle point, and the cross will appear in each of 
the facets. The needle itself will probably indicate the 
direction in which the cross should be moved in order to 
view it in the centre of the facets. The real secret lies 
not in focussing the facets themselves sharply, but in 
racking the body upwards until the cross comes into view, 
and focussing that sharply. 
Notes on Microscopy. 
F. SHILLINGTON SCALES, F. R. M. S. 
RoyvaL MIcROSscOPICAL SocrETy.—June 19th, William 
Carruthers, Esq., F. R. 8., President,in the chair. At the 
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