126 



THE MICROSCOPE AND ITS REVELATIONS. 



I'TO. 



Schiek's Compressor. 



it may be taken apart, either for cleaning or for the repair of a fracture 

 an accident to which the use of thin #lass of course renders it specially 

 liable. 



125. Compressor. The purpose of this 'nstrument is to apply a 

 gradual pressure to objects whose structure can only be made out when 

 they are thinned by extension, while their organization is so delicate as 

 to be confused or altogether destroyed by the slightest excess of pressure. 

 For the examination of such, an instrument in which the degree of 

 compression can be regulated with precision is almost indispensable. The 

 Compressorium represented in Fig. 100 was originally devised by Schiek 

 of Berlin; whilst its details were modified by M. de Quatrefages, who 



constantly employed it in 

 his elaborate and most suc- 

 cessful researches on the or- 

 ganization of the Marine 

 Worms. Being, however, 

 deficient in any provisions 

 for securing the parallelism 

 of the approximated sur- 

 faces, it has been superseded 

 ,jj other forms devised expressly with that view. In Ross's Improved 

 Compressor, shown in Fig. 101, the upper plate D is attached to 

 ? 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 in the lower 

 figure) is a square that slides into 

 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, to be replaced 

 in the Compressorium after the object 

 has been prepared for compression. 

 The only drawback to the use of this 

 instrument lies in the inconvenience of 

 using it in the reversed position so as 

 to look at the object from its under 

 side. This reversion is provided for in 

 the two forms of the instrument' made 

 by Messrs. Beck, which are shown in 

 Figs. 103, 104. In both, the upper 



FIG. 101. 



Ross's Improved Compressor, 



and the lower glasses are fixed, upon a plan devised by Mr. Slack, by 

 means of flat-headed screws, two to each glass (Fig. 103, A), the heads 

 fitting into holes of the opposite frame, so as to permit the close approxi- 

 mation of the two glass surfaces. In their Parallel Plate Compressor 

 (Fig. 102) the constant parallelism of the two plates is secured by the two 

 parallel bars, a, a; while the degree of their approximation and pressure 



