A NEW FORM OF POCKET MICROSCOPE. 
799 
from the object, or be turned away altogether when it is desired 
to use the instrument with direct light, after the manner of 
a telescope. 
A case to contain the microscope, with two slides and a 
piece of thin glass, occupies a very small space, being three 
inches and a quarter in length, one inch wide, one inch and 
an eighth in depth. A case of double the width will hold, 
besides the microscope and slides, an extra eyepiece and two 
objectives in boxes, one objective being always kept ready for 
use in the body of the microscope, a small glass tube or rod, 
and two dissecting needles. This case is considerably less 
cumbersome than the smallest pocket case of surgical instru¬ 
ments. 
In using the microscope the first step is to prepare the 
object in the usual way by placing it on the slide, adding a 
drop of water if necessary, and covering it with a piece of 
thin glass. The instrument is then to be taken in the left 
hand, the pins which project from the stage box are to 
be pulled back and the slide inserted into the space between 
the ring on the plug and the bottom of the microscope (as 
at c) ; the spring presses sufficiently to hold the slide firmly 
and allows of its being moved freely with the fingers. The 
mirror (g, Fig. 2), having been pulled out sufficiently, is in¬ 
clined towards the light, the draw tube (e) is pulled out about 
half its length, the body of the instrument (d) is then to be 
slowly moved downwards in the outer tube until the object 
is fairly in focus. The fine adjustment is obtained by mov¬ 
ing the draw tube (e). When the immersion lens is em¬ 
ployed the microscope may be conveniently turned up so 
that the bottom of the stage is towards the eye, and the body 
of the instrument may then be pushed upwards until the 
drop of water is seen to come in contact with the covering 
glass over the object. At this point the object will usually 
be sufficiently focussed to render the subsequent adjustment 
quite easy. 
For field work the small apparatus depicted in the plate 
at Fig. 3 will be found useful. The point may be pushed 
into the top of a gate-post or rail, and the microscope may 
then be clamped in the ring at the top, but generally it is 
more convenient to hold the instrument in the hand. 
The twelfth of an inch objective is the highest which has 
been tested, but from the ease with which this is worked 
there is no doubt that a twenty-fifth might be used with 
satisfactory results. 
Another form of portable microscope improved by Mr. 
Swift is shown in the next woodcut (Fig. 4). 
XLV. 
54 
