MAGNIFYING GLASSES. 
by moving the stage supporting the object to and from the lens : 
but when the instrument is applied to dissection, it is necessary 
to keep the subject dissected immoveable, and, therefore, not only 
to maintain the stage stationary, but to render it so solid and 
stable that it will bear the pressure of both the hands of the 
operator while he manipulates the dissecting instruments ; on this 
account the stage is often made larger than is represented in the 
figure, and supported by a separate pillar. 
The arm a carrying the doublet is also sometimes fixed in a 
square socket on the top of the rod g, so that it can be moved to 
and fro in the socket, while the socket itself can be turned upon 
the rod g ; by this combination of motions, the observer can with 
great convenience move the lens over every part of the object 
under examination. 
Simple magnifiers, with provisions similar to these, are made by 
the principal opticians, Messrs. Ross, Leland and Powell, Smith and 
Reck, Pritchard, Yarley, and others. 
When the object has not sufficient transparency to be seen by 
light transmitted through it from below, it may be illuminated 
by a light thrown upon it from above by a lamp or candle, and 
condensed, if necessary to obtain greater intensity, by means of a 
concave reflector or convex lens. 
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