METHODS OF RESEARCH: APPARATUS 



85 



slides bearing serial sections. These two were made, however, 

 since the great German war began, and this may be an incident 

 of it. The new pattern differs slightly also in other particulars 

 but so far as I can see is not better than the old, if as good. 



Objectives and Eyepieces. There is nothing better for 

 initial magnification than the Zeiss apochromatic objectives, 

 especially the superb 16-mm. and 8-mm. dry lenses (each of 

 which will give a clear image with a No. 

 12 eyepiece) and the 3-mm. 1.30 N. a. 

 and 2-mm. 1.30 N. a. homogeneous im- 

 mersion objectives, both of which have 

 a fairly long w r orking distance, especially 

 the 3-mm. 



If one has the 8-mm. apochromatic 

 objective and a No. 12 compensating 

 ocular, it is seldom necessary to use the 

 adjustable-collar Zeiss 4-mm. dry objec- 

 tive. We have several of them but they 

 cloud easily and, according to my experi- 

 ence, seldom give sharp images for any 

 great length of time. It is, I think, the 

 least useful of all the Zeiss objectives. 

 If higher powers than the 16-mm. or 8- 

 mm. are necessary, the student should 

 learn to use the oil immersion objectives. 

 We have also a Zeiss 2-mm. 1.40 N. a. 

 and a Zeiss 1.5-mm., but I seldom use 

 them. For use with these apochromatic 

 objectives several compensating eye- 

 pieces are furnished, the most necessary 



of which are the Nos. 4, 8, and 12. For research I generally 

 use the No. 8 or 12 eyepiece, the No. 18 is not necessary, and 

 for photomicrographic work the No. 4, in place of the special 

 eyepieces provided by Zeiss. 



Cheaper microscopes, but very good ones, are also made by 

 the Leitz Company, and by the Spencer Lens Company of 

 Buffalo, N. Y. 



FIG. 55. Zeiss Photo- 

 micrographic stand and 

 small upright camera. 

 Nearly all the photo- 

 micrographs in this book 

 were made with this 

 microscope and camera. 



