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On a Portable Field or Clinical Microscope. 
By Lionel S. Beale, M.B., F.R.S,, &c. 
(Eead December 10th, 1860.) 
This instrument was originally designed for microscopical 
investigation in connection with medicine, but it has been 
found applicable to microscopical inquiry generally. Its 
simplicity and cheapness strongly recommend it for the pur- 
poses of teaching. Lilce some other instruments which 
have from time to time been proposed_, it is composed of 
draw-tubes like a telescope ; but the arrangement of the stage, 
and the plan adopted for moving the slide, when different 
parts of the objects are submitted to examination, differ 
entirely, as far as the author is aware, from those usually 
adopted. The instrument consists of three tubes, a, b, c ; a 
carries the eye-piece, is four and a half inches long, and slides 
in b, which is of the same length, but only slides up to its 
centre in the outer tube c. Tube b carries the object-glass. 
There is a bolt on tube c, which can be fixed by aid of a rack 
and tooth, at any height, according to the focal length of 
the object-glass. This arrangement prevents the risk of the 
object-glass being forced through the preparation while being 
focussed. At the lower part of the body is a screw clamp 
for fixing the preparation in any particular position, and an 
aperture for throwing the light on opaque objects. The pre- 
p^aration is kept in contact with the flat surface below by a 
spring, which allows the requisite movements to be made 
with the hand. 
That part of the object which it is desired to ex- 
amine can easily be placed opposite the object-glass, if the 
instrument is inverted. Next, the focus is obtained by a 
screwing movement of the tube b; andif it be desired to examine 
any other parts of the object, this is easily effected by moving 
the slide with one hand, while the instrument is firmly grasped 
by the other. Delicate focussing is effected by drawing the 
tube a up and down. By this movement the distance be- 
tween the eye-piece and object-glass is altered. 
Any object-glass may be used with this instrument. I 
have adopted various powers, from a three-inch, magnifying 
fifteen diametres, to a twelfth, magnifying seven hundred 
diameters. 
In the examination of transparent objects ordinary day- 
light, or the direct light of a lamp, may be used ; or, if more 
convenient, the light may be reflected from a sheet of white 
paper, or from a small mirror inclined at the proper angle, 
and placed on the table. 
