ZOOLOaY AND BOTANY, MICROSCOPY, ETC. 835 



sets, and no difficulty in seeing what was the relative position of the 

 two layers. Having first ascertained the relation of structure, tJien 

 comes the opportunity for the perfect, non-penetrating, surface- 

 defining objective to get in its best work." 



Advantage of the Binocular.* — Professor Abbe remarks : — 



" The scientific value of stereoscopic observation will always 

 remain a matter of individual opinion. The skilled microscopist who 

 has become accustomed by years of practice to the solid interpretation 

 of superficial images, forms an idea with complete certainty at one 

 glance, or at most after a few turns of the adjusting screw, of the solid 

 structure of even very complicated objects. Such an observer will only 

 exceptionally desire any direct advantage from stereoscopic observation, 

 as, for instance, when viewing objects of unusual composition ; and 

 what has been said above (see ante, p. 687) shows that no stereoscopic 

 apparatus will ever make superfluous the acquisition of the art of 

 indirectly recognizing solid forms. 



" On the other hand, there is an advantage to be gained from 

 binocular vision, as such, which is quite independent of its stereoscopic 

 effect, and is in fact of imj^ortance precisely to those observers who 

 have least to expect from the latter. I have been told by many com- 

 petent microscopists in England that they use their binoculars when- 

 ever it is practicable, but not for the stereoscopic effect, but rather in 

 order to employ both eyes, and avoid the evil effects which the con- 

 tinual strain upon one eye in course of time occasions. I have also 

 found from my own experience that it would be well if regard were 

 paid to this. It can scarcely be doubted that continuous one-sided 

 vision by those who use the Microscope incessantly must gradually 

 diminish the ability to use the eyes for ordinary vision — for example, 

 in preparing objects and other work. From this point of view a 

 binocular arrangement may be of value to those for whom stereoscopic 

 observation is of subordinate interest." 



j3. Collecting', Mounting and Examining Objects, &c. 



Apparatus for Pond-life-t — Mr. E. T. Andrews describes an 

 apparatus for obtaining Entomostraca, &c., to obviate the cumbrous- 

 ness of the strained hand-net, off which it is difficult to get the animals 

 into a bottle readily. It does not require that one should put the net 

 over the bottle, and dash the water up, and so draw off' the animals, 

 nor is a separate vessel required in which to immerse the net. 



It consists of a tin tube If inches diameter, and 2^^ inches long, with 

 its front end turned over for strength and tinned ; the other end tapered 

 in f inch long to the size of the cork of the bottle, 2 oz. or 3 oz., em- 

 ployed, and a short length of about 4 inch of tin tube soldered thereon 

 to fit the cork, thus making the whole apparatus about 3^ inches long. In 

 the inside, rather more than half-way down the large tube, a ring of 

 strong wire is soldered and tinned ; a brass gas nipple is inserted from 

 the outside, and a ring of tin f inch in width is made to fit rather 



* Zeitschr. f. Mikr., ii, (18S0) p. 20. f ' Science-Gossip,' No. 199, p. 164. 



