COMPRESSORIUM. — DIPPING-TUBES. 



135 



chief defect in this apparatus consists in the absence of any pro- 

 vision for securing the parallelism of the approximated surfaces. 

 Such a provision is made in the improved Compressorium of 

 Mr. Ross, shown in Fig. 81, in which the upper plate d is attached 

 to a slide that works between grooves in the vertical piece c, so 

 that when raised or lowered by the milled-head it always maintains 

 its parallelism to the lower plate a. The thin glass carried by the 

 upper plate d (which can be turned aside on a swivel-joint, as shown 

 Fig. 82. * n * ne lower figure) is a square that slides into 



ABC grooves on its under side, so as to be easily 

 replaced if broken. The glass to which it is 

 opposed is a circular disk lodged in a shallow 

 socket in plate b, which is received into a 

 part of the lower plate a that is sunk below 

 the rest. The plate b carrying the lower glass 

 can be drawn out (as shown in the lower figure) 

 and laid upon the Dissecting Microscope, and 

 can then be replaced in the Compressorium after 

 the object has been prepared for compression. 

 100. Dipping -tabes. — 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. 82, but of 

 somewhat larger dimensions. These were for- 

 merly designated as ' fishing-tubes ; ' the pur- 

 pose for which they were originally devised 

 having been the fishing-out of Water-fleas, 

 aquatic Insect Larva?, the larger Animalcules, 

 or other living objects distinguishable either 

 by the unaided eye or by the assistance of a 

 magnifying-glass, from the vessels that may 

 contain them. But they are equally appli- 

 cable, of course, to the selection of minute 

 Plants ; and they may be turned to many other 

 no less useful purposes, some of which will be 

 specified hereafter. "When it is desired to 

 secure an object which can be seen either with 

 the eye alone or with a magnifying-glass, one 

 of these tubes is passed clown into the liquid, 

 its upper orifice haviDg been previously closed 

 by the forefinger, until its lower orifice is im- 

 mediately above the object ; the finger being 

 then removed, the liquid suddenly rises into 

 the tube, probably carrying the object up with 

 it"; and if this is seen to be the case, by put- 

 Dipping-tubes. ting the finger again on the top of the tube, 



