548 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



serve to fix the position of any point of interest. Both screw-heads are 

 placed on the left so as to leave the operator's right entirely free. 



Fig. 129. 



Koristka's Hand Magnifiers.* — The loup shown in fig. 130 has two 

 pairs of two achromatic cemented lenses. The mount of the upper works 

 in a thread so that its distance from the lower pair can be altered. In this 

 way the magnifying power can be varied from 5 to 10 diameters. The 

 field in each case is flat and lar°:e. 



Fig. 130. 



* F. Koristka's Catalogue, Milau, fig. 50, p. 64. 



