58 PHOTOMICROGRAPHY 



jective, are evidenced by the appearance of the colour 

 fringes on either side of the lines under suitable con- 

 ditions of illumination. Apochromatic objectives, when 

 used with compensating oculars, give practically no 

 colour, while a good achromat gives only slight fringes. 



Finally, it is practically impossible to pick out the 

 objectives of any one maker as better than those of 

 others. The output of any of those whose microscopes 

 have been mentioned can be relied upon as being of the 

 highest class. The following have been used to make 

 the photomicrographs from which the illustrations are 

 taken : 



Achromatic Objectives 



3" by Clarke and Page . . N.A. 0-12 



2" Crouch .... ; , 0-13 



36mm. Seibert (No. 0) . . 0-11 



I" Swift .... 0*25 



16mm. Leitz (No. 3) . . ,, 0'30 



1" Swift .... ,, 0*88 



I" ,, Watson (Parachromatic) ,, 0'74 



4 mm. ,, Leitz (No. 6) . 0'82 



3-2 mm. (No. 7) . v . . 0-85 



T V" ,, ,, (oil immersion) . ,, 1*30 



iV" Baker, Leitz, and Swift (do.) 1'30 



Apochromatic Objectives 



16 mm. by Zeiss . . . . N.A. 0*30 



4 . ; . . 0-95 



3 ., (oil immersion) . ,, 1*40 



2 ., Zeiss and Leitz (do.) . 1'30 



Micro- Anastigmats 



25 & 50 mm. Micro -planars by Zeiss 

 75 mm. ,, , ,, Ross 



3" Anastigmat (No. 0) by Aldis 



