546 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
To use this instrument, the stand with the slide figured above in 
position on its stage is placed on the circular disc B, with the centre of 
the hemispherical lens as nearly over the centre C as possible. The 
objective whose aperture is to be measured is focused on the centre of 
the hemispherical lens, the Microscope being in a horizontal position. 
A light — e. g. a small incandescent lamp — is then placed at a convenient 
distance in front of the Microscope, and the Microscope and disc revolved, 
and the angle of aperture in crown glass read off, as with other aperto- 
metres. The eccentricity is eliminated by taking the mean of the two 
readings at E and F. 
I should have been glad to include more objectives in this table, 
but have been unable to procure them, some dealers apparently being 
unwilling to submit their objectives to the test proposed, since no 
attention was paid to my letter requesting the loan of objectives for said 
purpose. The table needs no explanation. No tests of the objectives 
were made other than to determine their aperture.” 
C6) Miscellaneous. 
Solution of the Dust Problem in Microscopy.* — Mr. A. H. Cole 
says : — “ The statement of the dust problem is this : Given a stock of 
cleaned micro-slips and cover-glasses, to keep them clean and ready for 
use at any moment, without the necessity of brushing or wiping them. 
The following solution is the result of a laboratory study of the problem, 
and is now announced after having received the approval of leading 
microscopists. 
The objects to be accomplished are : — 
(1) To secure a dust-proof magazine for storing the cleaned micro- 
slips and cover-glasses in separate compartments for the different sizes 
of squares, circles, and oblongs. 
(2) To provide simple mechanical appliances for removing a single 
slip or cover without exposing those remaining in the case. 
(3) To provide an automatic device for warning the operator of the 
approaching exhaustion of his stock of any of the shapes of covers and of 
slips, thus avoiding the necessity of opening the case, except to replenish 
stock. 
(4) To provide against the breaking or disarrangement of the covers 
in case of the accidental overturning of the case. 
(5) Incidentally to provide a mounting-table, with guides for cen- 
tering the objects and cover-glasses, the whole apparatus being so con- 
structed that the glasses are not touched by the fingers, and only once 
by the forceps until the slide is completed and labelled. 
The dust-proof slip and cover-glass case fully meet these require- 
ments. The case is 4J in. square on the base, and 6 in. high. The 
slips and mounting-table are contained in the lower half, and the cover- 
glasses in the upper portion. The mounting-table has concentric lines 
for guidance in properly centering the objects. Four dust-excluders 
are hinged to the front of the grooved table to protect the slots through 
which the cover-glasses pass out upon the grooved table. The milled 
head of the roller which pushes the cover-glasses out of the slots is at 
* Amer. Natuialist, xxvii. (1893) pp. 405-7 (3 pis.). 
