ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 665 



issued, enlarged and revised, and with additional chapters on the general 

 Morphology and Physiology of Bacteria, &c. There are seventy-three 

 additional illustrations, and. a very extensive Bibliography. 



FiELu, A. G. — A new Photomicrographic Apparatus. 



Amcr. Moil. Micr. Journ., VIII. (1887) p. 94 (1 fig.). 

 Hitchcock, P. — Besolution of pearls of Amphipleura. 

 [Note on Dr. Van Heurck's photographs.] 



Amcr. Mon. Micr. Journ., VIII. (1887) pp. 105-6. 

 M AGIN I, G. — Qualche considerazioni sulla micro-fotografia. (Some considerations on 

 photomicrography.) Boll. R. Accad. Med. JRomn, 188G, No. 4. 



Mercer, A. C. — Photomicrograph tws?«s Microphotograph. 



[" A photomicrograph is a macroscopic photogr.aph of a microscopic object ; a 

 microphotograpli is a microscoijic photograph of a macroscopic object." Tlie 

 distinction was originated by Mr. George Shadbolt in 1859 or I860.] 



Proc. Amcr. Soc. Micr., 9th Ann. Meeting, 1886, p. 131. 

 Microphotogrammes du Dr. Van Heurck et du Dr. P. Francotte. (Pliotomicrographs of 

 Dr. Van Heurck and Dr. P. Francotte.) 



[3 of Amphipleura pcllucida resolved into beads. NavicuJa fusca and Nobert's IStb 

 and 19th band. 4 of zoological subjects.] 



Bull. Soc. Behj. 3ficr., XIII. (1887) pp. 159-60 (1 pi.) 

 Photomicrography. — See (6) American Society of Microscopists. 



(5) Microscopical Optics and Manipulation. 



Method of determining the index of refraction when the refracting 

 angle is large.* — The method of minimum deviation can only be employed 

 when the refracting angle of the prism is less than twice the limiting 

 angle ; but Siguor G. Bartalini shows that indices may be measured in a 

 prism bounded by three j)lanes inclined to one another at two unequal 

 angles, the ray of light being so transmitted as to be refracted at the first 

 and third and internally reflected at the second surface. For the success 

 of this method it is only necessary that the larger angle of the prism added 

 to the complement of the limiting angle should be less than 180°. 



The formula is 



sin a 



sin 



where cot (p = cot (a — /?) cos^ 6 



. „ sin b 



sm' 6 = 



sin a . cos (a — fj) 



sin 6 

 cr cot (p = ^ 



sin a . sin (a — )8) . cos^ 6^ 



tan^0'="-^i^^l^i^. 

 sm 



According as the ray after internal reflection makes an acute or an obtuse 

 angle with the third surface. 



In the above formulae a and b are the angles of incidence and emergence, 

 and a and (3 are the corresponding angles of the prism. 



Observations made upon a quartz crystal gave — 



By minimum deviation ,. .. n„ = 1*544:2 % = 1*5537 

 By the above method .. .. ?i„ = 1-544:4 n, = 1-5535. 



Resolution of 200,000 lines to the inch. — Once again microscopists 

 have been doomed to a bitter disappointment, which is the harder to bear 



* Atti Soc. Toscana Sci. Nat., v. (1887) pp. 181-3 (1 fig.). 

 1887. 2 X 



