THE COMPOUND MICEOSCOPE. 77 



micrometer, frog-plate, vial-holder, small and large condens- 

 ing lens, steel disc a substitute for the camera lucida, 

 polarizing prisms, and many other important pieces of appa- 

 ratus, and the price varies from forty to seventy guineas, 

 depending upon the number of the powers and the apparatus 

 attached thereto; the powers themselves range from the 

 two inch to the one-sixteenth, and magnify from 20 to 2,500 

 diameters. 



A second microscope, constructed by Messrs. Powell and 

 Lealand, and known by its being mounted on three legs, is 

 described in the London Physiological Journal, page 63, and is 

 represented in Plate 2. The three legs inclined, as seen in 

 the figure, support, at their upper part, the trunnions to 

 which the tube, J, and the stage are attached. From out the 

 tube, J, a triangular bar is raised by a rack and pinion con- 

 nected with the large miUed head, A. To the upper part of 

 the triangular bar a broad arm is fixed, bearing the compound 

 body ; this arm is hoUow and contains the mechanism for the 

 fine adjustment, which is effected by turning the milled head, 

 B. The arm is connected with the triangular bar by a strong 

 conical pin, on which it turns, so that the compound body 

 may be moved aside from the stage when necessary. The 

 stage is similar to that described in the preceding instrument, 

 and is capable of being moved from side to side by the milled 

 head, C, and up and down by that at D. When both are 

 turned together,' a diagonal movement is produced, the axis of 

 D is carried through to the opposite side of the stage, where 

 there is another milled head, so that, if necessary, both hands 

 may be employed at the same time. The achromatic con- 

 denser is represented as fixed into its place at the bottom of 

 the stage, where also may be seen an arm, E, for the stops or 

 dark wells. The mirror, G, and the spring clip to the stage, 

 H, are aU similar to those described in the former instrument. 

 In order to render the compound body exceedingly steady, 

 two small rods, springing from the arm, are attached to the 

 back part of the body a Httle above the centre. To this 

 microscope, as well as to the preceding, aU the apparatus 

 there mentioned can be fitted. The stand itself is not so 



