334 The Microscope. • 



With the same arrangement of light no resolution was gained upon 

 a balsam mount of this test. No sub-stage fittings were then tried, 

 but enough had been seen and not seen to beget the disappointment 

 mentioned. The objective is non-adjustable; yet the evidence was 

 not wanting of the need of correction. My tube-length being also 

 practically fixed, there was no chance to try the effect of change 

 in this. Putting the instrument aside for the time without enthu- 

 siasm upon its possession, I waited several days for a more favorable 

 opjiortunity of better testing its merits. 



Besides the mark for tube-length already quoted, there is en- 

 graved upon the objective: " Homog. Immers," "2.0 mm, Apert. 

 1.40." "Carl Zeiss, Jena," and "88"— the latter on the bevelled 

 front, presumably the serial number of manufacture. The total 

 length of the mounting, exclusive of screw, is only one and a quar- 

 ter inches, the lower half nickle-plated. The oculars received are 

 mai-ked: "12, 22.5 mm," and "8, 34 mm." That is, one increases 

 the magnifying power of the objective twelve times and the other 

 eight times. They are mounted in nickel (or nickel-plate) with 

 double diaphragms below, the outer one limiting the field to three- 

 fourths of an inch in diameter for the " 8 " ocular and nine-sixteenths 

 for the "12." They are very heavy from the amovmt of metal used 

 in mounting. Over the eye-lens is screwed a curious cap with its 

 central opening high above the glass — five- sixteenths of an inch in 

 the "8." In my use of this ocular I was obliged to keep the eye 

 considerably above the cap, fully an inch from the upper surface of 

 the lens. There also came with the others a " projection ocular " 

 (marked " ") of a very different construction and mounting. I 

 have not tried this for its special purpose. 



The screw of the objective does not fit well in the Bullock and 

 some of Bausch and Lomb stands, though it does in a Zeiss stand 

 ordered with the "society screw." It also does in Beck's instru- 

 ments tried. 



At the first leisure hours I returned to the critical examination 

 of the a})paratus and have now to detail results so far as ascertained. 

 Haying observed especially that the structural details of a test object 

 came in best view at a focus considerably above that of the outline, 

 indicating need of correction for thickness of cover, I replaced the 

 tube of the Bullock stand by one made for photographic use. This 

 has a draw -tube moved by rack and pinion. When the new objec- 

 tive was screwed in, the distance from the back lens to the upper 



