OP THE MICROSCOPE. 135 



ployed may be regulated by the thickness or number of semi- 

 rings of rubber placed between the glass plates. 



By means of the three screws with milled nuts, the trough 

 may be taken to pieces in a few seconds, and as easily put to- 

 gether. In this way it is easy to clean the inside of the glass 

 plates, to replace broken ones, etc., etc. 



The Weber Slide. This ingenious device consists of a 

 common slide, rather thicker than usual, m the centre of which 

 an annular groove has been ground, as shown in Fig. 34. The 

 central part of the cell is left nearly the full original height of 

 the glass just enough being taken off to allow of a thin layer 

 of liquid between it and the cover-glass. Any liquid contain- 

 ing minute forms of animal or vegetable life having been laid 

 on the top of the central elevation, will be held there by capil- 

 lary attraction as soon as the cover is laid on, and if the latter 

 be cemented round the edges, an air-tight aquarium on a 

 minute scale is formed, in which, if the proper balance of 

 animal and vegetable life is present, the objects may be kept in 

 good condition for a long time. We have kept one of these 

 slides for weeks with desmids, diatoms, and minute forms of 

 animal life, all in good condition. The proper cement for at- 

 taching the cover to these slides is beeswax softened with oil. 



B 



Pig. 34. THE WEBER SLIDE. 



The Weber slide is a very handy and convenient piece of ap- 

 paratus, but it is difficult to obtain. We have, therefore, used 

 the following form, which anyone can make for himself. 



The Cell Trough. The simplest trough in which living 

 objects may be kept for some time, is constructed out of an 

 ordinary cell and thin cover, as shown in Fig. 35. If we 

 have a liquid containing some very minute objects which we 

 wish to keep for some time in a condition suitable for examina- 

 tion, we place a drop on the centre of a thin cover-glass, which 

 must be larger than the cell. A very small cover is then placed 



