ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 559 



regulator of the current. If expense is not an object four accumu- 

 lators may be used (requiring sixteen elements), the accumulators 

 thus serving both as regulators and reservoirs, and allowing several 

 lamps to be used at a time. The particular Swan lamps he uses are 

 the "2^-candle" lamps. 



Still later Dr. Van Heurck says that he is experimenting with 

 some new accumulators of M. de Kabath, which seem likely to give 

 good results. 



Black Backgrounds.*— Mr. Tuffen West on principle very much 

 dislikes to see objects mounted with an irremovable black back- 

 ground. When it is desirable to view objects as opaque, there are so 

 many other ways of doing this ; e. g. the diaphragm, the dark-well, a 

 piece of dead-black paper, clotb, or velvet placed behind the slide. 

 The object can then still be viewed as a transparent object also. 

 Otherwise it is the mounter saying to the observer, " You shall see 

 my slide as I will, and in no other way." 



Micrometrical Measurement by means of Optical Images.!— A 

 paper on this subject was published some time since by Professor 

 Abbe in German, and we at once had it translated with a view to its 

 insertion in this Journal. We must frankly confess, however, our 

 inability to put the paper in proper form for publication here, and as 

 Professor Abbe is much taxed in various ways we have not thought 

 it right to ask him to undertake the matter. 



We therefore content ourselves with a translation of a German 

 abstract of the article. % 



" E. Abbe has turned his attention to the study of the Microscope 

 as used with a micrometer, and finds that the sources of error belong- 

 ing to the present methods of measurement can be obviated by using 

 ' telescopic ' systems of lenses instead of the ordinary objective with a 

 finite focal distance. Such a glass is made up of two separate lenses 

 or systems, whose focal planes are turned towards each other and 

 coincide. It has an unlimited focal length, and the focal points lie 

 at an infinite distance ; all objects are reproduced with an enlarge- 

 ment which may be determined at will, but is constant ; so that this 

 magnification remains independent alike of the distance of the object, 

 that of the image, and of the length of the tube." 



Malassez's Improved Compte-globules. — Professor L. Malassez 

 in 1880 published § a detailed paper on corpuscle-counters in which 

 the various devices of himself, Hayem and Nachet, Gowers and Zeiss 

 were fully referred to with a statement of their respective advantages 

 and disadvantages, and in which he described an improved apparatus 

 suggested by himself. An epitome of the paper by Mrs. Ernest Hart 

 with critical observations has also appeared in English, || so that it 

 is unnecessary to refer to it otherwise than briefly here. 



* Journ. Post. Micr. Soc, i. (1882) p. 94. 



t SB. Jenaisch. Gesell. f. Med. u. Naturw., 1879, p. xi. 



j Jahresber. (Virchow and Hirscli) for 1879, p. 27. 



§ Arch, de Physiologie, 1880, p. 377. 



|| Quart. Journ. Micr. Sci., xxi. (1881) pp. 132-45 (3 figs.). 



