OF MICKOSCOPIC OBJECTS. 63 



if necessary, without being shaken or interfered with, other- 

 wise uniformity of dispersion will be prevented. When 

 thoroughly dry, a thin ring of one of the adhesive varnishes 

 gold-size will be found as good as any may be drawn 

 round the diatoms, and allowed to dry in a slight degree. 

 The slide and thin glass cover should then be warmed and 

 the latter gently pressed upon the ring of varnish until the 

 adhesion all round is complete. 



As some of the diatoms require object-glasses of extremely 

 high power, and consequently short focus, to show them, 

 they must be as close to the outer surface of the cover as 

 possible. For this reason they are sometimes placed upon 

 the under side of the thin glass, as follows. Clean the 

 surfaces of the slide and cover, and with the rod or pipe 

 place the liquid containing the diatoms upon the thin glass, 

 and dry as before. Trace the ring to receive the cover upon 

 the slide, and when almost dry, warm both and proceed as 

 above. Whichever of these methods is employed, the outer 

 ring of coloured varnish may be applied as elsewhere described 

 and the slide finished. 



Diatoms are also sometimes mounted betwixt two thin 

 glasses, as described in Chapter II., so that the light by 

 which they are examined may receive as little interference as 

 possible, and that an achromatic condenser may be brought 

 into focus under the slide. 



Of the various modes of cleaning and mounting Diato- 

 maceae, I believe that the following may be safely recom- 

 mended, as affording results of the best quality. My friend, 

 Mr. T. G. Eylands, gave it to me as that which he prefers, 

 and I can safely say that his numerous slides are at least 

 equal to any I have ever seen. I will give it just as I 

 received it from him, though there may be some little 

 repetition of what has been said elsewhere, as he does not 

 appropriate any part of it as his own. He says : In this 

 branch of mounting, general rules alone can be laid down, 

 because the gatherings may contain iron, lime, fine silt, or 

 vegetable matter under conditions for special treatment, and 



