DESCRIPTION OF DR. GORING's ENGISCOPE. 175 



Figure 19 is a small cone, to slide over the object- 

 glass when acting by plain artificial light. 



Figure 20 is the arm by which the optical part of the 

 AmicianCatadioptric Engiscope* is attached to the present 

 stand : it must be considerably longer than the other, 

 and, like it, racked to its extremity, to admit of its being 

 taken out of the socket. By means of its swivel and 

 pinching-screw, it allows the body to turn round, 

 and present itself either in front or at the sides of the 

 stage. 



Figure 21 is the aquatic live-box, with an extra pierced 

 lid, 'm, for aerial insects and land objects, &c. There 

 should be about half a dozen of these, of different sizes, 

 varying from that given in the plate, to about 2-10ths of 

 an inch in diameter. It would be found a convenience 

 if the larger ones had watch-glasses fixed into them with 

 their curves applying to each other, and their concavi- 

 ties pointing outwards, instead of the plane glasses, as 

 given in the drawing ; for by this arrangement, when 

 used with very low powers for exhibiting a grand melee of 

 aquatic insects, &c., taking in nearly their whole area, 

 the edges of the field will be as distinct as its centre; 

 the foci of these two parts of the visible superficies being 

 always different with &flat object, and a low power, even 

 with the best aplanatics. 



The glasses, whether flat or concave, must be well 

 cemented into their cells by painters' ground white lead 

 or opticians' cement, that the box may be completely 



* MicrograpLia, chap. i. 



