ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



797 



claimed priority over that of Prof. Harting (p. 799) shown in fig. 131. 

 The prisms of Mr. Ahreus's Tri-ocular Microscope (p. 799) are shown 

 in fig. 132. 



Fig. 129. 



Fig. 130. 



Heukck, H. van. — Le Microscope Anglo-Continental ou Microscope d'Etndiant 

 de M. "Watson and Sons. (Watson and Sons' Anglo-Continental or Student's 

 Microscope.) 



[Includes also a photomicrograph ic apparatus.] 



Journ. de Micr., XI. (1888) pp. 314-8 (2 figs.). 

 Seaman, W. H. — American and Foreign Microscopes. Science, XI. (1888) p. 120. 



K2j Eye-pieces and Objectives. 



Zeiss's "Compensation Eye-piece 6 with 1/1 Micron-division."* — 

 The graduation of the eye-piece micrometers hitherto made is arbitrary, 

 and has no intimate connection with the magnifying power of the objec- 

 tives used with them for micrometric measurement. For this reason it 

 is necessary to have a table giving the value of an interval for each 

 objective and eye-piece ; for example, the interval may be — 



"With eye-piece 2, for objectives A, C, E, and 1/12 = 16, 6-7, 2-7, 

 1-82 /t. 



With eye-piece 3, for the same objectives = 14, 6-0, 2*4, 1'67 /x. 



If, then, the image of an object observed with a 1/12-in. homo- 

 geneous-immersion objective covers 3-75 intervals of the micrometer 

 eye-piece 2, the true dimension is 3*75 x 1"82 = 6*82 /x. 



* From the description issued by Dr. Zeiss. Cf. also K. Schliephacke in Flora, 

 Ixxi. (1888) pp. 33-44. 



