ACCESSORY APPARATUS. 



127 



is regulated by the screw I, which works out of centre in a conical hole 

 of the lower frame, so that, the further it is introduced, the more closely 

 the two frames, with their glasses, are approximated. This pattern works 

 equally well whichever side is uppermost. In the Reversible Cell Com- 

 pressor of the same makers (Figs. 103 B, 104) the upper glass is held down 

 by a ring a, which screws-on to that which bears the lower one, giving 

 any degree of pressure that may be required. When screwed together, 

 they form a cell that fits into the plate #, and is attached to it by the 

 milled-head c; by unscrewing which the cell can be instantly detached 

 and replaced in a reverse position. In all these Compressors, it is easy 

 to vary the thickness qf the glass within convenient limits; and the ob- 



Fra. 102, 



Era. 105. 

 ABC 



Beck's Parallel Plate Compressorium. 



Tic. 103. 



Beck's Reversible Cell Compressorium. 



Dipping Tubes. 



Glass Syringe. 



server should be always provided with a stock of glass slips and disks of 

 the requisite sizes and of different thicknesses, suitable to the kind of 

 investigation he may be prosecuting. As thin glasses, when used for 

 compression, are very liable to fracture, the power of immediately re- 

 placing them without the employment of cement (as in Mr. Slack's con- 

 struction) is a great convenience. 



126. Dipping Titles. In every operation in which small quantities 

 of liquid, or small objects contained in liquid, have to be dealt with by 

 the Microscopist, he will find it a very great convenience to be provided 

 with a set of Tubes of the forms represented in Fig. 105, but of some- 



