ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



1029 



pratiques. (Ke'surue of the public kcture on the processes of reproducing with 

 printing inks photoniicrographic cliches and images of scientific objects. Description 

 of a new method of photolithogiaphv, with practical demonstrations.) 



Bail. SVx-. B<'hj. M:-r., XIII. (1887) pp. 182-5 (1 pi.). 



Hex SEX, V.— Ein pliotograpliisclies Zimmer fiir Mikroskopiker. (A photographic room 

 for mieroscopists.) Kulliker's GrahdationscArift, 1887, pp. 61-71 (1 pi.). 



KiXG, Y. M. — The Photomicrography of Histological Subjects. 



Jonrn. of Jf/cr., VI. (1887) pp. 205-16, from New York Med. Jo'irn. 



Marktaxxer, G.— Bemerkungen iiber Mikrophotographie. (Remarks on photo- 

 micrography.) Phot. Corresp., 1887, p. 237. 



C5) Microscopical Optics and Manipulation- 



Microscopical Tube-length, its length in millimetres, and the parts 

 included in it by the various opticians of the world.* — Prof. S. H, Gage 

 read a paper with the above title to the Pittsburg Meeting of the American 

 Society of Mieroscopists. 



" lu the construction of microscopic objectives, the corrections must be 

 made for the formation of the image at a definite distance, or, in other 

 words, the tube of the stand of the Microscope on which the objective is to 

 be used, must have a definite length. Consequently, the microscopist must 

 know and use this distance or ' microscopical tube-length ' to obtain the 

 best results in using the objective in practical work. 



In order to obtain the exact distance in millimetres for which objectives 

 are corrected, and the parts of the Microscope included in this distance or 

 ' tube-length,' the following questions were submitted to all the opticians of 

 the world whose addresses could be obtained : — 1. For what ' tube-length ' 

 do you correct your microscopic objectives? Please give the length in 

 millimetres or inches. 2. Please indicate on the diagram on the opposite 

 page (fig. 247) exactly what parts of the Microscope you include in ' tube- 

 length.' From nearly all precise and satisfactory answers were received, 

 and I wish to express here my appreciation of their courtesy. The answers 

 received are given below, and indicated on the accompanying diagram. 



Table giving Length in Millimetres and showing parts included in 

 Length ' hy various Opticians. 



Tuhe- 



Parts included in 

 ' Tube-length.' 

 See Diagram. 



a-d . . 



a-d 



b-d 



«-17 

 c-d 

 e-e 



c'-e 



' Tube-length ' in 

 millimetres. 



Grunow, New York .. ... .. .. 203. 



Nachet et Fils, Paris 146 or 200. 



Powell and Lealand, London .. .. 254. 



C. Eeichert, Vienna 100-180. 



W. Wales, New York 2-54. 



Bausch & Lomb Optical Co., Eochester 216. 



Bezu, Hausser et Cie., Paris .. .. 220. 



Klonne und Miiller, Berlin .. .. 160-180 or 254. 



W. eS: H. Seibert, Wetzlar 190. 



Swift & Son, London 165 to 228^. 



^C. Zeiss, Jena 160 or 250. 



^Gundlach Optical Co., Rochester .. 254. 



Eoss & Co., London 254. 



E. & J. Beck, London 254. 



H. E. Spencer & Co., Geneva, N.Y. .. 254. 



J. Green, Brooklyn 254. 



E. Leitz, Wetzlar 12-5-180.. 



For Oil-immersions .. 160. 



* Microscope, vii. (1887) pp. 289-92 (1 fig.). 



