194 



THE MICROSCOPE. 



piece of glass like the bottom of a live-box. This piece 

 of glass is set in a frame B, which slides in and out so 

 that it can be removed for the convenience of preparing 



any object upon it 

 under water if de- 

 sirable. The upper 

 movable part I) is 

 attached to a screw- 

 motion at C ; and at 

 one end of the brass 

 plate A, which forms 

 the bed of the in- 

 strument, is an up- 

 right piece of brass C, grooved so as to receive a ver- 

 tical plate, to which a downward motion is giyen by a 



FIG. 130. Ross's Compressorium. 



FIG. 131. Beck's Parallel-plate Compressor. 



single fine screw, surrounded by a spiral spring, which 

 elevates the plate as soon as the screw-pressure is re- 

 moved. 



Beck's Parallel-plate Compressor, fig. 131, affords a 



FIG. 132. Botterill's Live-trough. 



more exact means of regulating the pressure, and can be 



used for a variety of purposes. It is also easily cleaned. 



Lire-troughs are made to partake of a variety of 



