32 PREPARATION AND MOUNTING 



used there is no necessity for the edges of the slide tp bo 

 " ground," as all danger of scratching, &c., is done away with by 

 the paper cover. 



Many now use paper covers, about one and a half inches long, 

 on the upper side\of the slide only, with the centre cut out as 

 before, with no otherVpurpose than that of hiding the edge of the 

 thin glass where it is united to the slide. 



The method of " finismfig," however, which is mostly used at 

 the present time, is to lay a coating of varnish upon the edge of 

 the thin glass, and extend it some little way on the slide. When 

 a black circle is required, nothing serves the purpose better than 

 the gold-size and lampblack, or the asphalt and india-rubber var- 

 nish, neither of which is liable to chip ; but when used for this, 

 the latter should be rather thinner, as before advised. Some of 

 these varnishes are preferred of different colours, which may be 

 made by using the different kinds of sealing-wax, as described in 

 Chapter I. ; but they are always liable to the defects there men- 

 tioned. This circle cannot be made in any other way but by one 

 of those contrivances which have now centred in Shadbolt's turn- 

 table. A very little practice will enable the young student to 

 place his slide so that the circle may be uniform with the edge of 

 the thin glass. 



The slide is now complete, except the addition of the name 

 and any other particulars which may be desirable. For this 

 purpose one of the methods described in Chapter I. must be 

 employed. 



Amongst the various classes of microscopic objects now receiv- 

 ing general attention, the Diatomacese may be placed in a promi- 

 nent position. They afford endless opportunities of research, 

 and some very elaborate works have already been issued concern- 

 ing them. Professor Smith's may be mentioned as one contain- 

 ing, perhaps, the best illustrations. The young student may wish 

 to know what a diatom is. The " Micrographic Dictionary" 

 gives the following definition : " A family of confervoid Algae, 

 of very peculiar character, consisting of microscopic brittle organ- 

 isms." They are now looked upon by almost all of our scientific 

 men as belonging to the vegetable kingdom, though some few still 

 assign them to the animal. They are almost invariably exceed- 



