ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 445 



Oberhauser's camera by a mirror, the eye-piece by a single lens, and 

 the small prism by a reflecting glass plate or a mirror, a convenient 

 instrument is obtained which will not necessitate the inclination of 

 the Microscope. 



Rogers's New Eye-piece Micrometer.* — " Professor W. A. Rogers, 

 of Harvard Observatory, has again laid microscopists under obligation 

 by making an eye-piece micrometer for high oculars. It is a cover- 

 glass of proper size to fit above the diaphragm of a 1/2 in, or 3/8 in. 

 ocular, ruled in a scale with the fifth and tenth lines longer, and so 

 fine as to need the magnifying power of the eye-lenses to separate 

 the lines well. The high-power ocular separates also the strias of 

 diatoms, or other minute subdivisions of objects, and the scale enables 

 one to count them with a readiness and ease which has not before 

 been possible. It is a simple and inexpensive thing, that takes the 

 place of the most expensive spider-web micrometers." 



Geneva Co.'s Nose-piece Adapters.— Thury Adapters.— Prof. M. 



Thury takes exception to the remark at p. 284 that these adapters do 

 not " differ in principle from the nose-pieces of Nachet and Verick." 



The first adapter was, he says, made in October 1863 after his 

 designs for Count Castracane, and another in 1865 for Prof. E. Clapa- 

 rede. A Microscope exhibited by the Geneva Co. at the Paris Exhibition 

 in 1867 was fitted with a similar adapter and was accompanied by a 

 written description. At the 1878 Exhibition the modified movable 

 form was exhibited. M. Nachet, who adopted the fixed form in 1877, 

 " loyally termed it the ' Pince-Thury.' " It was after the 1878 

 Exhibition that the movable form came to be made by others. 



Prof. Thury's apparatus was evidently therefore the precursor of 

 all such contrivances. 



Selection of a Series of Objectives.— Several writers have pub- 

 lished their views on this subject, differing (with the exception of Dr. 

 Carpenter) more or less from those put forward by Prof. Abbe in his 

 paper on the " Eelation of Aperture and Power." 



Dr. G. E. Blackham f selects " as a set of powers sufficient for all 

 the work of any microscopist the following : — 



One 4 in. objective of 0- 10 N.A. = 12° air angle nearly. 

 One 1 in. objective of 0'26 N.A. = 30° air angle nearly. 

 One 1/6 in. objective of • 94 N.A. = 140° air angle nearly. 

 One 1/8 in. objective of 1 • 42 N.A. 



The first two to be dry- working objectives without cover correc- 

 tion, the third to be dry-working with cover correction, and the fourth 

 to be a homogeneous-immersion objective with cover correction, and all 

 to be of the highest possible grade of workmanship. The stand . . 

 to be furnished with six eye-pieces, viz. 2 in., 1 in,, and 3/4 in. 

 Huyghenian, and 1/2, 1/3, and 1/4 in. solid. The following table 



* Amer. Mon. Micr. Journ., v. (1881) p. 52. 



t Proc. Amer. Soc. Micr., 6th Ann. Meeting, 1883, pp. 33-41, 227-31. 



