250 THE HISTORY AND DEVELOPMENT OF THE MICROSCOPE 



30 times, and, employed in such a stand as fig. 202, they are ad- 

 mirably adapted for picking out minute shells or for other similar 

 manipulations, the sand or dredgings to be examined being spread 

 upon a piece of black paper, and raised upon a book, a box, or some 

 other support to such a height that when the lens is adjusted 

 thereto, the eye may be applied to it continuously without unneces- 

 sary fatigue. It will be found advantageous that the foot of the 

 microscope should not stand upon the paper over which the objects 

 are spread, as it is desirable to shake this from time to time in order 

 to bring a fresh portion of the matters to be examined into view ; 



P2 



FIG. 201. Greenougb's binocular, arranged as a dissecting microscope (1897). 



and, generally speaking, it will be found convenient to place it on 

 the opposite side of the object, rather than on the same side with 

 the observer. In a suitable position these lenses with their holder 

 may be most conveniently set for the dissection of objects contained 

 in a plate or trough, the sides of which, being higher than the lens, 

 would prevent the use of any magnifier mounted on a horizontal 

 arm. Although the uses of this little instrument are greatly 

 limited by its want of stage, mirror, &c., yet, for the class of pur- 

 poses to which it is suited, it has advantages over perhaps every 

 other form that has been devised. Where, on the other hand, 



