80 PRACTICAL TREATISE ON THE MICROSCOPE, 



which the object-glasses are attached, is slowly raised or de- 

 pressed. The mirror, F, is made to slide up and down the 

 tube, D E, and being mounted on a semi-circular arm, can be 

 turned in every possible direction. 



One great value of this microscope is its extreme portability, 

 as the whole apparatus, consisting of the above described 

 instrument, together with four object-glasses, two eye-pieces, 

 animalcule cage, dark stops, forceps, &c., can be packed in a 

 box, the internal measurement of which is nine inches long, 

 five broad, and two deep. 



Besides the three preceding microscopes of Messrs. Powell 

 and Lealand, there are two others made by them requiring 

 especial mention. The first of these is of large size, and 

 consists of a heavy tripod base, from which rises a short stout 

 pillar, having a cradle joint at its summit, to which is attached 

 a triangular bar, fifteen inches in length, and each of its 

 sides one-inch-and-a-quarter broad. To the middle of this 

 bar a stage, seven inches square, is fixed ; it has the same kind 

 of adjustments as those of the smaller instruments, being made 

 also on Mr. Turrell's plan, and, from being of large size, 

 the hands of the operator do not interfere with the object 

 when adjusting it. The milled heads for effecting the adjust- 

 ment are placed in a line, so that one hand only is required to 

 move the stage in two directions. The compound body is 

 firmly supported on the upper half of the triangular bar by a 

 frame which fits the bar accurately and is made to move 

 smoothly up or down by rack and pinion turned by two milled 

 heads; the compound body is also capable of being turned 

 away from over the stage by means of a joint in the frame 

 supporting it. The fine adjustment is made by an endless 

 screw and two inclined planes ; it has also two milled heads, 

 only two inches apart from the coarse, but both horizontal 

 and parallel with them; by this means, the hand may 

 be passed from one to the other very readily. To the 

 lower part of the triangular bar is adapted the mirror, which 

 is of the same construction as that previously described, but 

 capable of being moved up and down on the triangular bar 

 by rack and pinion; the achromatic condenser is attached 



