crouch's student's binocular. 71 



Second-class Binocular Microscojies. 



48. For some time after the Stereoscopic Binocular Microscope 

 was first successfully brought into action, it was commonly 

 regarded as a sort of article de luxe, better fitted for the purposes 

 of display than for those of research. Its value in Scientific 

 investigation, however, is now admitted by all who have really 

 worked with it upon suitable objects ; and so strongly is the 

 Author impressed with its advantages, that he would earnestly 

 recommend every one about to provide himself with even a Second 

 class Microscope, to incur the small expense of the Binocular addi- 

 tion. This addition, however, will lose an important element of 

 its value, if the Stage of the instrument be not adapted to rotate 

 in the optic axis of the Body ; so that objects which are being 

 viewed by incident light may be presented to the illuminating 

 rays in every direction. This rotation not only gives most valuable 

 aid in the appreciation of the solid form of the object, by the play 

 of light and shade among the inequalities of its surface ; but also 

 frequently brings into view features that would otherwise have 

 escaped notice, either from having been previously thrown into 

 shadow by some neighbouring prominence, or from not receiving 

 their light at the angle at which they could most advantageously 

 reflect it. And as it may be readily introduced into the construc- 

 tion of any Microscope, either on the plan of MM. Nachet which 

 has been just described, or on that of Smith and Beck's ' Popular ' 

 Microscope to be presently noticed, the Author anticipates that it 

 will ere long be adopted in almost every form of Stereoscopic 

 Binocular. 



49. Crouch's Student's Binocular. — This instrument was devised 

 at a time when the construction of the Binocular was still almost 

 exclusively confined to the makers of First-class instruments ; and 

 it had the great merit of bringing within reach of the Student a 

 convenient and well-constructed Binocular, at a cost not greater 

 than that usually charged for the addition of the Wenham prism 

 and Secondary body alone. "With the improvements it has since 

 received, it still remains one of the best instruments of its class ; 

 and the Author, after considerable use of it, can strongly recom- 

 mend it to such as desire to possess a Binocular at once cheap, 

 good, and portable. Its general arrangement, as shown in Fig. 38, 

 corresponds closely with that of the small Microscope of the same 

 maker already described ; the double body being supported on a 

 'limb' on the Lister model. The adjustment of the Eye-pieces 

 for the distance of the eyes is made by a transverse bar which is 

 attached to one of them, and which -works through a slot-piece 

 fixed to the other ; so that if by the application of the finger 



two Eye-pieces, and three Objectives, giving a range of powei's from 

 25 to 400 diameters, is only 225 francs, or about £'J. The price of thu 

 Stereo-pseudoecopic apparatus is 175 francs, or £7 additional. 



