ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 417 



whether the appearance of relief that it gives is necessary to enable us 

 to form a correct idea of the true shape of objects in which the appear- 

 ance of relief is most striking — the answer must be a decided negative. 

 It is true that the binocular does reveal more of the form of an object 

 at the first glance than the monocular ; but it is a matter of experience 

 that those who use only one eye in microscopical work, never make 

 the mistake of supposing that an object is flat merely because it seems 

 to be so. A very short experience enables one to form a perfectly 

 correct idea of the shape of any object by a few turns of the focussing 

 screw. Hence, persons whose means are limited, and who desire to 

 invest a small sum of money in a Microscope to be used for purposes 

 of study, would do well to forego any thought of purchasing binocular 

 stands. 



" On the other hand, there are certain qualities of binoculars which 

 commend them to all workers who can afford the additional cost. 

 Apart from any stereoscopic effects it is doubtless true that the use 

 of two eyes whenever possible renders continued observation less 

 tiresome than when only one can be applied to the tube. Some 

 writers have stated that with a monocular one eye is overstrained 

 while the other is not used at all, contending that by using the 

 binocular that trouble is overcome. The two eyes should be used 

 alternately with the monocular, hence they ought to become trained 

 for sharpness of vision, but we doubt if the binocular aids in the way 

 assumed, for we are inclined to believe that although both eyes are 

 simultaneously employed with the binocular, the right eye does most 

 of the real work, the left eye only supplementing its fellow and giving 

 the binocular effect. However this may be, there is a certain ease in 

 working with binoculars which doubtless makes the strain upon the 

 eyes less than with monoculars. 



" The stereoscoj)ic effects, while not of great practical importance 

 as already stated, certainly render many objects more attractive to 

 look at. For this reason a Microscope for the entertainment and 

 instruction of friends should certainly be a binocular." 



Mr. G. E. Fell also discusses the binocular Microscope and stereo- 

 scopic vision,* and the objections that have been made to such instru- 

 ments, at the same time describing the Powell and Lealand, Nachet, 

 Wenham, Tolles, H. L. Smith, Abbe, and Barnard forms. He is 

 inclined to believe that a trifling temporary defect in the faculty of 

 consentaneous focalization may be produced by the continued use of 

 one eye with the monocular, so that the microscopist may be really 

 incapacitated for realizing the advantage or effect of stereoscopic 

 vision with the binocular, but he does not agree that the convergence 

 of the tubes produces an unnatural straining of the lateral recti 

 muscles, as the angle of that convergence is about equal to that of the 

 eyes in ordinary observation at 10 to 12 inches. 



Professor Hamilton L. Smithf prefers the Nachet binocular, though 

 he considers that the Wenham binocular " is beautifully simple in 

 theory and, except for one thing, perfect in practice. The one great 



* Proc. Amer. Soc. Micr., 1881, pp. 69-83 (8 figs.), 

 t Ibid., pp. 89-91. 



