ZOOLOGY AND BOTANY, MICROSCOPY, ETC, 335 



degrees of exposure, and the author has no hesitation in stating that 

 the method advocated is superior to that of any of the usual cameras. 

 The arrangement he adopts consists of a heavy bench, 8 ft. long by 

 20 in. wide, having two shelves of the same length and width below for 

 apparatus. The legs stand upon thick pads of felt to minimise vibra- 

 tion ; the weight of the bench with its load of apparatus keeping the 

 whole firm and rigid. Upon one end of the bench stands the dark 

 chamber, 3 ft. long, 6 ft. high, and as wide as the bench. This chamber 

 is provided with large light-proof ventilators above and below, as it 

 contains the illuminant as well as the Microscope. The front of this 

 chamber is left open to a height, from the floor of the room, greater 

 than the head of the worker in order to give him access to the contained 

 apparatus. When everything is ready for an exposure a light-proof 

 curtain is let down across the opening. The eye-piece end of the 

 Microscope protrudes at one end of the chamber through a velvet tube, 

 and the projected image is caught on a focusing-screen held on an 

 adjustable easel that can be placed in any position on the unoccupied 

 portion (5 ft.) of the bench. There is an ingenious rod and pulley 

 arrangement for focusing which is worked from the dark-room. As an 

 illuminant the author recommends a good paraffin oil lamp for all 

 ordinary work ; it fulfils every requirement as the light given by it is 

 far more actinic to the photographic plate than is generally recognized. 

 The author also strongly recommends the English form of Microscope 

 with a tripod foot, and is a firm believer in its advantages over the 

 continental pattern. 



An interesting and useful chapter is that describing the making 

 of a photomicrograph, wherein, by means of a dialogue, "Young 

 Castlebuilder " is trained in the way he should go, by the guidance of 

 " Old Surefoot." Other chapters deal with the vertical camera ; special 

 methods of illumination ; list of photographic necessities ; chemicals 

 and formulae for solutions ; list of useful books. There are some six 

 plates of beautiful photomicrographs, and an elaborate table, giving 

 under fifteen heads all the details of filters, exposures, plates, etc., by 

 which they were produced. 



Lord, H. C. — The Making of a Photographic Objective. 



[A description of a Course in Applied Optics offered at the Emerson 

 McMillin Observatory of the Ohio State University.] 



Ohio Journ. Sci., xvi. (1915) pp. 3-16 (7 figs.). 



(5) Microscopical Optics and Manipulation. 



Microscopical Experiment.*— E. M. Nelson describes the follow- 

 ing interesting microscopical experiment : — A Microscope is set up 

 with a stage micrometer, with O"! mm. on stage; a micrometer eye- 

 piece, having a scale of equal parts in the focus of the eye-lens of a 

 Huyghenian eye-piece, is used ; this scale can be moved nearer or 

 farther from the eye-lens of the eye-piece for adjustment to the 

 observer's sight ; it, therefore, differs from those of the ordinary small 



• English Mechanic, ciii. (1916) p. 271. 



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