On a Portable Field or Clinical Microscope. 

 By Lionel S. Beale, M.B., F.R.S., &c. 



(Read December 10th, 1860.) 



This instrument was originally designed for microscopical 

 investigation in connection with medicine, but it lias been 

 found applicable to microscopical inquiry generally. Its 

 simplicity and cheapness strongly recommend it for the pur- 

 poses of teaching. Like 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- 

 paration 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 movementof 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. 



