ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



97 



SO 



that no condenser system 



is 



Is the shortness of time-exposure, 

 required.* 



Illumination, and the Use of the Condenser in Histological Micro- 

 graphy.f — A. B. Lee sums up his paper on this subject with the fol- 

 lowing advice : — : " If you desire to work with daylight, which I do not 

 advise, put an object on the slide, turn the mirror so as to illuminate it, 

 focus, centre the condenser, if it is not already centred for the objective 

 to be used, set the diaphragm, and focus the condenser on a bar of the 

 window. Afterwards never touch the diaphragm, nor the condenser 

 rackwork. 



" If you desire to use a lamp without bnll's-eye, put it exactly in its 

 marked position on the table, turn the edge of the flame towards the 

 Microscope, put a coloured screen in front, 

 turn the plane mirror so as to illuminate the 

 condenser, centre the condenser, orientate 

 the mirror so as to centre the flame-image, set 

 the diaphragm, and focus the condenser. 

 Afterwards never touch the diaphragm or the 

 condenser, but regulate the light, if necessary, 

 by your coloured screens. 



" If you desire to use the bull's-eye, which 

 I regard as the normal arrangement for a 

 cytologist, proceed at first exactly as above, 

 then place the bull's-eye before the flame. Its 

 focal distance from the flame and its azimuthal 

 position having been once for all fixed by stop- 

 screws, it will be in adjustment as soon as it 

 fully illuminates the mirror, and it will be 

 only necessary to slightly correct the orienta- 

 tion of the latter for getting the exact cent- 

 ring of the flame-image, and to re-focus the ^^^S^ 

 condenser for its new light-source. As be- 

 fore, never afterwards touch the diaphragm 

 nor the condenser rackwork, but regulate the 

 light, if necessary, by coloured screens." 



Illuminating Apparatus for Metallo- 

 graphy 4 — 1. Electric Incandescent Lamp. — 

 This is shown in fig. 20, and is of 150 



candle-power, with Edison base, socket, binding-posts, _ stand, and 

 elevating-screws. It is used with a large biconvex condensing lens. 



2. 00° Automatic Focussing Electric Arc Lamp.%— This (fig. 21) is 

 used for projection or for photomicrography. It yields from 2000 to 



* This method of illumination for visual purposes was exhibited before the 

 Society, January 1883; it proved a complete failure, the definition being such as 

 would" satisfy no one but the merest beginner, Joum. R.M.S., 18S3, p. 29, figs. 1-G. 

 It was reinvented in 1885 and 1886, v. Journal for those years, p. 303, figs. 48-54, 

 and p. 1053, fig. 222. 



, t La Cellule, xix. 2nd fasc. (1902) pp. 405-31 (1 pi.); also as a pamphlet. 



t Catalogue of the Boston Testing Laboratories, p. 10, fig. 14. 



§ Loc. cit., pp. 16-8, fig. 16. 



Fig. 20. 



Feb. 18th, 1903 



H 



