4«.)i; 



SUMMARY OF CURRENT RESEARCHES RELATING To 



Huyghen's ocular with variable thread distances ; the field can be 

 variously stopped off (as in model A). There are three objectives, giving 

 about 10-100 diameters. Focusing is by rack-and-pinion, and the 

 ocular is rotatory through 00°. 



Fig. 126. 



Vogel-Campbell's Large Measuring Microscope (Model III.). — 

 This instrument (fig. 120), $b in the maker's catalogue, resembles 

 model II. in its horseshoe mount and hinged pillar, inclinable through 

 90°. But it differs essentially from the other types in its retention of 



* Otto Toepfer und Sohn's Catalogue (Neue Astrophysikalische Apparate, 

 1908), Potsdam. 



