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 anil 

 Beck, 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. 



112 



