104 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Binocular Microscope . — Take for the objective glass a lens equally 
convex on all sides, of a diameter 80/100. The principal focus will he 
at a distance 40/100. Now remove the object a little beyond this dis- 
tance, so that the rays behind the objective lens can converge to form 
an image. This image will be much larger than the object (as we have 
shown in formula 2 ), for at double the distance it will be equal to the 
object itself, and from double the distance till you reach the focus it 
(the image) will always be larger, till at the focus there will be no 
image at all, because there the rays behind the lens are parallel. The 
object placed beyond double the distance of the focus always makes the 
image less and less than the object, till it is placed at so great a distance 
that rays falling upon the lens are considered parallel and the image is 
found in the distance of the principal focus. All this has been already 
shown elsewhere. Behind this greater image two other ocular lenses 
are placed. One near the image itself is exceedingly convex on all sides, 
of a diameter 25/100. This arrangement shows the object very large 
and a little farther 
I' IG 4 away than in ordinary 
composite Microscopes 
p SP shown in cap. 2. 
On account of 
lengthening the tube, 
or the greater distance 
of tho lenses from each 
other (if a similar 
arrangement be made 
for both eyes), both 
eyes can easily look at 
one and the same ob- 
ject. The two ‘prios ’ 
lenses, ocular lenses, 
should be as far apart 
as is the distance be- 
tween the two eyes, 
and all else arranged 
as in binocular tubes 
already explained. 
Such a Microscope in 
its external form may 
be like the one shown 
in tho figure, where 
A B is the case. W ith- 
in are the two tubes, 
arranged as we have 
already shown in treat- 
ing of binoculars. The 
object to be looked at 
is jdaced at C.” 
Binocular Perimicroscope.* *— This instrument, devised by Aubert, 
is practically Westien’s binocular lens with much increased magnifying 
* Pfliiger’s Arcbiv, xlvii. (1890) pp. 341 6 (2 figs.). 
