MICROSCOPIC OBJECTS. 151 



The best cement for fixing objects on these mountings 

 is mastic varnish. These mountings are held in the 

 forceps by the pin ; if the forceps are large, they should 

 have a hole made through their sides, to secure the head 

 of the pin, which is otherwise liable to slip out : it also 

 enables us to turn the object about the head as a centre 

 without any risk of its escaping ; see s. in fig. 23 of 

 ' Microscopic Illustratrons.' The cylinders may be made 

 of various sizes and arranged in cabinets, the bottom of 

 the drawers being covered with cork about a quarter of 

 an inch thick, into which the pins are inserted. The 

 blank end of the cylinder should have a number painted 

 in white, corresponding with another in the list of the 

 names. When arranged in the drawer all the pins should 

 be sHghtly inclined in one direction with their numbered 

 ends up wards,, which enables you readily to take out any 

 object by referring to the list, and also protects the 

 objects from dust falling upon them. A vast number of 

 objects by proper arrangement wall thus occupy very little 

 space. 



(12.) On Preparing very Diaphanous Bodies. — In all 

 cases it is desirable to mount an object permanently; but 

 it sometimes happens that while we eifect this purpose, 

 the object becomes obliterated and lost to vision. This 

 occurs when mounting an object in a fluid,- as for example 

 Canada balsam : if it is of the same colour and refractive 

 power as the balsam, the rays of light will not be bent in 

 passing in and out from the one to the other. When 

 this is Hkely to happen, the object must be slightly 



