OPTICAL INSTRUMENTS. 



171 



Engraver's Magnifier (Fig. 605), larger size, in cocoa 

 wood frame. 



Price, $1.00 



Extra large, 

 ..75. 



Engraver's Double Lens Magnifier. 

 (Fig. 666.) The engraver's dou- 

 ble lens magnifier consists of two 

 plano-convex, or periscopic lenses, 

 mounted with their convex sides in- 

 ward, in a brass frame, the cells 

 unscrewing to clean the glasses oc- 

 casionally. This construction of 

 magnifier is preferable for persons in 

 constant use of these glasses, and 

 desirous of straining their eyes as 

 little as possible in the use thereof, 

 there being less spherical aberration 

 in two lenses thus arranged than in 

 others. Price, $1.50 and $1.75. 



Hand Magnifiers. -(Fig. 667.) 

 This consists of a convex lens, mount- 

 ed in a metal frame, and attached to 

 a long handle, by which it may be 



