SMITH AND BECK'S POPULAR MICROSCOPE. 73 



regards as so important, by a modification of MM. Nachet's 

 stage, which the maker of this instrument constructs for such as 

 desire it. As the rotating disk, in Mr. Crouch's construction, 

 works upon a short tube, instead of being imbedded in the fixed 

 stage, this stage is not as thin as that of MM. Nachet. and 

 therefore does not admit of the employment of light direct from 

 the Mirror of as great obliquity. But the central tube may be 

 made to carry any required fittings ; and the ' Webster Con- 

 denser,' with the excentric diaphragms hereafter to be described 

 (§ 80), may be easily made to give rays of almost any degree of 

 obliquity that may be required ; whilst a fine adjustment may be 

 attached to the body for use with high powers. — This instrument, 

 however, is not so much intended for the resolution of difficult 

 objects, as it is for the Scientific investigations and general studies 

 which can be earned on by means of moderate powers ; to such 

 it is quite as well adapted as instruments of far higher cost, whilst 

 its portability and simplicity render it especially suitable for Sea- 

 side use, particularly when fitted with the Glass stage. 



50. Smith and Bectis Popular Microscope. — For the general 

 purposes of Microscopists, and especially for such as work with low 

 and moderate powers upon objects for the study of which Binocular 

 vision is peculiarly advantageous, there is probably no instrument 

 more suitable than the one represented in Plate hi., which was 

 devised by the late Mr. R. Beck. Its chief peculiarity consists in 

 the ingenious mode in which it is framed and supported ; a mode 

 which peculiarly adapts it to the requirements of Travellers, as 

 enabling it to bear a good deal of rough usage without injury. 

 The Stem to which the stage d and the mirror e are attached, and 

 which contains the racked bar c that carries the arm b and the 

 binocular body A, is itself attached by a pair of centres to the 

 broad stay g, which again is attached by a pair of centres at its 

 lower angles to the triangular base p. The lower end H of the 

 stem carries a stout projecting pin, which fits into various holes 

 along the medial line of the base ; whereby the instrument may 

 be steadied in positions more or less inclined, or may be fixed 

 upright. It may be also fixed in the horizontal position required 

 for drawing with the Camera Lucida (§ 71) ; for the pin at the 

 bottom of the stem then enters the hole at the top of the stud k, 

 and the stay G falls flat down, resting on the top of the stout pin 

 L. The advantages of this construction are that it is strong, firm, 

 and yet light ; that the instrument rests securely at the particular 

 inclination desired, which is often not the case on the ordinary 

 construction when the joint has worked loose ; and that in every 

 position there is the needful preponderance of balance. The Stage 

 D is circular, and upon it fits a circular plate t, which rotates in the 

 optic axis of the Microscope ; the special advantage of this rotation 

 for Binocular study has been already pointed out (§ 48). On the 

 plate t there slides the Object-holder u, which is so attached to it 



