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On a SuBpMERSION Microscorse. By R. E. Dupcron, M.D. 
For the examination of minute aquatic vegetable and 
animal organisms in a considerable quantity of their native 
element, it is desirable to have a microscope which can be 
plunged into water without affecting its optical qualities. 
The ordinary microscopes are only intended for use in an 
aérial medium, and were we to insert the end of the object- 
piece into water we should at once destroy the magnifying 
power of the object-glass to a considerable extent, and run 
the risk of injuring the brass work and screws constituting 
the mechanism of the object-piece. 
For some time past I have endeavoured to devise a micro- 
scope which should enable me to study objects in a consider- 
able depth of water without injuring the instrument or 
destroying its magnifying power. I need not detail the 
various plans that successively occurred to me for effecting 
this object, but will only describe the means by which we 
can convert an ordinary microscope for viewing objects in an 
aérial medium into a microscope for observing objects beneath 
the water, without in any way injuring it for its original 
purpose. 
Over the object-piece I screw a brass or other metal tube, 
elosed at the further end by a disc of plain glass, cemented 
into its place so as to be perfectly water-tight. The length 
this tube projects beyond the inferior surface of the object- 
glass must, of course, be less than the focus of the latter. 
Thus, if the object-glass have a focus of one inch, I find it 
best not to have the enveloping tube projecting more than 
half an inch beyond the object-glass. If the focus of the 
object-glass be 4 inch, the tube should not project more than 
+ inch beyond it. 
A microscope so protected may be plunged into water as 
deep as the protecting tube will admit, with scarcely appre- 
ciable loss of magnifying power, and with no loss of distinct- 
ness of definition or illumination of the object. This arrange- 
ment possesses great advantages over the ordinary “ tank 
microscope,” in which the microscope is suspended above 
the water, and not intended or fitted for submersion. For 
while with this latter instrument the least movement of the 
_ table or tank causes a tremulous motion of the surface of the 
water, which distorts all objects seen below it, by my 
arrangement the distinctness of the image is not marred by 
any agitation of the surface of the water. The glass disc of 
