FOR BALSAM MOUNTING. 47 



are necessary, and when in use they firmly clip the slide only^ their 

 four points resting against the edges, not on the top of the 

 covering glass. In this way the cover is perfectly firmly held in 

 position ; it is impossible for it to slip out of place, while no 

 pressure is applied to the object. In applying them to the slide 

 they are first clipped on anywhere, and then pushed up until their 

 points touch the edges of the thin glass circle ; this can ge?ierally 

 be accomplished without shifting the latter perceptibly. The 

 slide can then be handled with perfect impunity, no matter 

 how soft the balsam may be, and a good deal of the superfluous 

 balsam may be removed if care be taken not to displace the clips. 

 The balsam may then, if advisable, be hardened under more or 

 less heat, and I find the top of a hot-water cistern is a first-rate 

 drying ground for the purpose. After about a fortnight in such a 

 position, even slides mounted in ordi?iary balsam will generally 

 be found sufficiently hard to be cleaned with perfect safety, but 

 theoretically it is evident that the time taken to harden under the 

 cover is the same as the time taken to harden in an open vessel 

 by a layer of balsam whose thickness is one quarter the diameter 

 of the covering glass. When the balsam is fully set the points of 

 the clips will be firmly stuck down on the slides, but there is no 

 difficulty in pulling them off; if necessary, the wires might be 

 heated, but this is not required. 



I now make the clips of brass wire, the length required for 

 each being about 2^ inches. It is advisable to make the clips of 

 different sizes to accommodate the different sizes of cover-glasses, 

 and, properly, the distance between the points of the clip should 

 be about seven-tenths of the diameter of the covers for which it is 

 made. For use with some mounts it is convenient to bend the 

 points of the clip inwards, while if the object be a very thick one 

 the points turned down will be found very useful. Where 

 neither of these things is done, I file off the ends at a suitable 

 angle so that they hold the edges of the cover more firmly ; but 

 different microscopists will probably introduce different modifica- 

 tions in the form of the clips to suit their own fancy. 



With this paper I am sending a pair of the clips, so that the 

 Editor may be able to try them on a glass slip with the cover 

 merely laid on. My only wonder is that this simple and, withal 

 effectual contrivance was not thought of long ago. 



