202 



THE AMERICAN MONTHLY 



[November, 



son's binocular works well, although 

 it requires a tube of special con- 

 stiniction which cannot be also used 

 as a monocular. 



In the above described ai'i'ange- 

 ment of Dr. Abbe, however, all 

 these defects or objections are over- 

 come. It will be observed that the 

 plan differs from all oth*ers in that 

 the beam of rays from the objective 

 is not bisected, but by a symmetri- 

 cal division of the rays hj partial 

 reflection, which may be effected at 

 any part of their course, the neces- 

 sary conditions for binocular vision 

 are secured. The binocular eye- 

 piece can be used with any desired 

 magnification, and can be made to 

 give either stereoscopic or pseudo- 

 scopic effects, at pleasure, by the 

 use of suitable diaphragms in or 

 above the oculars. The intensity 

 of the reflected rays is scarcely j4, 

 while that of the axial ray is about 

 ^ of the entire light ; but this con- 

 siderable difference in the bright- 

 ness of the two images is not only 

 not a defect in the apparatus, but is 

 a real advantage, for experience 

 has shown that the production of a 

 good stereoscopic effect requires 

 one perfect and clear picture, be- 

 side which the other may, without 

 noticeable detriment, be far less 

 perfect, and it is to be presumed 

 that the same result would follow 

 any difference in brightness. More- 

 over, one eye is more sensitive to 

 light than the other, and the dif- 

 ference in the intensity of the 

 two images is an advantage, on 

 account of this physiological pecu- 

 liarity. 



Rubber Cell for Opaque Objects. 



Mr. II. F. Atwood has invented 

 a new kind of cell for opaque 

 mounting, which we illustrate this 

 month. The following account is 



taken from the circular with which 

 Mr. Atwood has favored us : — 



"A considerable experience in 

 mounting opaque slides during the 

 past few years has convinced me 

 that much of the labor incident to 

 it could be avoided, if a cell of 

 suitable material and shape could 

 be produced at a nominal cost. 

 This, I think, has now been at- 

 tained, and ] take pleasure in sul)- 

 mitting one for which I claim con- 

 venience, cheapness, and general 

 utility. With it the amateur can 

 produce a slide fully as perfect, and 

 with as great a degree of neatness 

 as can the professional. The cell is 



Fig. 28. 



of hard rul)ber, highly polished, and 

 of attractive shape ; the base is 

 solid, thus giving a black back- 

 ground of ru])ber ; around the to^) 

 is a ledge fitted to receive a one- 

 half inch cover-glass ; tliis, being 

 secured by a trifle of shellac, or 

 any similar cement, completes the 

 mounting. The cell may be at- 

 tached to a glass slip by any cement, 

 before or after preparation. For 

 exchanges it offers superior advan- 

 tages, inasmuch as the cell, with 

 objects enclosed, may be sent 

 through the mails independent of 

 the glass slips, the recipient attacli 

 them. In this way a saving is 

 made in postage, and no risk of 

 loss by slips being broken in transit. 

 They wall solve the jwoblem 

 which often perplexes the student 

 or collector who is crowded for 

 cabinet room. Many objects for 

 future reference may be mounted 

 in this simple cell, numbered and 

 put aw^ay without a slide, a cabinet 

 drawer holding two hundred of 

 them, while but forty slides could 

 be acconnnodated in the same 

 space." 



