322 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



made of two pieces of thin sheet brass beut in the maimer shown in 

 the woodcut. 



Two other dissecting Microscopes are shown * in fig. 74 (Schieck's) 

 and fig. 75 (Bocker's), in which a Briicke lens in a slightly varied 



Fic. 75. 



form is employed. None of the English dissecting Microscopes are, 

 so far as we know, provided with other than single lenses or the older 

 form of doublet. 



Standard Eye-pieces. — The Committee appointed by the 

 American Society of Microscopists f to report on the nomenclature 

 and sizes of oculars, brought up a further report at the last 

 (Rochester) meeting.^ 



The Society adopted the original recommendation of the Com- 

 mittee for 1 • 25 in. as the standard size of tube (with a preference of 

 1 • 00 or 1 • 35 in. where other sizes are required), and • 75 in. for cap- 

 tubes (for interchange of camera lucidas, &c.), and 1 • 50 in. for sub- 

 stage tubes, all outside measure. They also adopted the following 

 resolution on nomenclature, somewhat varied from the Committee's 

 suggestion in their first report. 



" Eesolved that this Society recommends that oculars be named by 

 the equivalent focal lengths in English inches, representing their 

 actual power in use in the compound Microscope with objectives of 

 not more than 1/4 in. equivalent focus, and with a working tube- 

 length of 10 in. including the mounting of the objective, on the basis 

 of 1-in. focus corresponding to 10 diameters of amplification." 



The Report of the Committee on which the resolution was founded 

 was as follows : — 



" The naming of oculars. Wee objectives, by their equivalent focal 

 lengths in inches, hut estimated in a conventional manner at a somewhat 

 arbitrarily chosen distance. This is an attempt to secure in the case 

 of oculars an approximate and serviceable nomenclature having some- 



* Lowenbcrz's Bericht u. d. Wiss. Instr. a. >\. Berliner Gewerbeausstellung, 

 1880, p. 295 (1 fig.). Dippel's ' Das Mikroskop,' 2nd ed., 1882, p. 186 (1 fig.), 

 t See this Journal, iii. (1883) p. 711. 

 i Proc. Amer. Soc Micr., 7tli Ann. Meeting, 1884, pp. 228-33 (1 fig.). 



