[_CH. 



MA GNIFICA TION AND MICRO ME TR Y 



121 



lines. If the ocular micrometer has some quite narrow spaces, and others consid- 

 erably larger, one can nearly always manage to exactly include the object by some 

 two lines. The ocular screw micrometers (Fig. 106-107) obviates this entirely as 

 the cross hair or lines traverse the object or its real image, and whether this 

 distance be great or small it can be read off on the graduated wheel, and no 

 estimation or guess work is necessary. 



For those especially interested in micrometry, as in its relation to medical 

 jurisprudence, the following references are recommended. These articles consider 

 the problem in a scientific as well as a practical spirit : The papers of Prof. Wm. 

 A. Rogers on micrometers and micrometry, in the Amer. Quar. Micr. Jour., Vol. 

 !> PP- 97 > 2 8 ; Proceedings Amer. Soc. Microscopists, 1882, 1883, 1887. Dr. M. 

 D. Ewell, Proc. Amer. Soc. Micrs., 1890 ; The Microscope, 1889, pp. 43-45 ; North 

 Amer. Pract., 1890, pp. 97, 173. Dr. J. J. Woodward, Amer. Jour, of the Med. 

 Sci., 1875. M. C. White, Article "Blood-stains," Ref. Hand-Book Med. Sciences, 

 1885. Medico-Legal Journal, Vol. XII. For the change in magnification due to 

 a change in the adjustment of adjustable objectives, see Jour. Roy. Micr. Soc., 

 iSSo, p. 702 ; Amer. Monthly Micr. Jour., 1880, p. 67. Carpenter-Dallinger, p. 270. 



If one consults the medico-legal journals ; the microscopical journals, the 

 Index Medicus, and the Index Catalog of the Library of the Surgeon General's 

 Office, under Micrometry, Blood, and Jurisprudence, he can get on track of the 

 main work which has been and is being done. 



f in. 



Dry objectives of 16 mm. (f z. ), 4. mm. (i in.) and homogeneous immersion 

 objective 0/2 mm. ( T V in. ) in their mountings. (Bausch & Lomb Opt. Co.). 



