LEVER STAGE OBJECT-FINDER. 129 



traverse, not merely horizontally or vertically, but, by the simul- 

 taneous sliding of both plates, in any intermediate direction. 

 This is especially convenient in following the movements of Ani- 

 malcules, &c., for which purpose this lever-stage is to be pre- 

 ferred to the ordinary form : its use being attended with this 

 particular facility, that, as the motion of the hand is reversed by 

 the lever, so that the object moves in the opposite direction, and 

 as the motion of the object is again reversed to the eye by the 

 microscope, the image moves in the same direction as the hand; 

 and thus, with a little practice, even the most rapid swimmer 

 may be kept within the field by the dexterous management of 

 the lever. For general purposes, however, the ordinary tra- 

 versing stage will be found most convenient. 



53. Object- Finder. Either kind of movable stage admits of a 

 simple addition, which very much facilitates the " finding" of 

 minute objects mounted in slides, that are not distinguishable by 

 the naked eye ; such, for example, as the particular forms that 

 present themselves in Diatomaceous deposits. This "finder" 

 consists of two graduated scales, one of them vertical, attached 

 to the fixed stage-plate, and the other horizontal, attached to an 

 arm carried by the intermediate plate ; the first of these scales 

 enables the observer to " set" the vertically sliding plate to any 

 determinate position in relation to the fixed plate, while the 

 second gives him the like power of setting the horizontally sliding 

 plate by the intermediate. In order to make use of these scales, it 

 is of course necessary that the sliding and rotating platform on 

 which the object immediately rests, should be always brought 

 into one constant position upon the traversing plates beneath ; 

 this is accomplished by means of a pair of stops, against which it 

 should be brought to bear. So, again, this sliding plate or ob- 

 ject-platform should itself be furnished with a "stop" for the 

 glass slide to abut against, so as to secure this being always laid 

 in the same position. These stops may be made removable, so 

 as not to interfere with the ordinary working of the stage. Now 

 supposing an observer to be examining a newly-mounted slide, 

 containing any objects which he is likely to wish to find on some 

 future occasion; he first lays the slide on the object-platform, 

 with its lower edge resting on the ledge, and its end abutting 

 against the lateral stop, and brings the object-platform itself into 

 its fixed place against the stops ; then if, on sweeping through 

 the slide, he meet with any particular form worthy of note, he 

 reads off its position upon the two scales, and records it in any 

 convenient mode. The scale may be divided to 50ths of an inch, 

 and each of these spaces may be again halved by the eye ; the 

 record may perhaps be best made thus, Triceratiu m favus f | t ; 

 the upper number always referring to the upper scale, which is 

 the horizontal, and the lower to the vertical. Now whenever 

 the Microscopist may wish again to bring this object under exa- 

 mination, he has merely to lay the slide in the same position on 



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