USE OF THE HAND MAGNIFIER 17 



close to the spectacle glasses.) This matter may be 

 remedied by the use of one of the following holders : 



1 . Suggested Lens Holder for Laboratory Use. — A piece of 

 sheet brass or aluminum is cut into the form of a spectacle 

 frame, with two unequal circular apertures. The lens is 

 fitted into a tight sleeve in the smaller aperture ; and a disc 

 of ground glass, 30 or more millimeters across, fastened over 

 the larger aperture (Fig. 3). If the distance between the 



Fig. 3.- — Plan (reduced) of a lens holder with a ground-glass disc on the left 

 and a low-power corrected magnifying lens on the right. The point of the 

 attachment for the handle is shown on the right. This lens holder can also bo 

 arranged to fold into a pocket case. The blackened marginal ring round the 

 lens helps to exclude lateral light when the eye is close to the lens. 



center of the lens and the center of the ground glass is 65 

 millimeters, there will be room in the width of the ground 

 glass for the usual variations in interpupillary distance from 

 55 to 75 millimeters. A handle is arranged to be screwed 

 on at one end ; and by reversing the lens, if necessary; either 

 the right or the left eye can be used. 



2. Suggested Lens Holder for the Pocket. — The lens holder 

 (Fig. 3), without the handle, is to be fitted into a case of 

 brass or aluminum, which serves as a handle. For both 

 the lens holders, three different lenses may be used. The 

 lenses should be mounted so as to fit into the same sleeve. 

 An achromatic planoconvex doublet magnifying about 3 

 times, and two Steinheil triplets with magnifications of 

 about 6 and 10, may well be available. 



Forms of Lenses. — For the low magnifications of 3 and 

 4 times a planoconvex achromatic doublet (Fig. 1) gives 

 good results. This magnifying lens is to be held so that 

 the eye looks always through the center of its flat side. To 

 attain this, the lens and head are constantly moved in 

 relation to the object (or the object is moved to and fro). 



