OBSERVING WITH AND MANAGING ENGISCOPE. 197 



act upon its extremity, and give the rotatory movement 

 which was before performed by the wheel, &c. More- 

 over, whenever the lengthening piece is in use for trans- 

 parent objects not contained in fluids, the shade (fig. 18) 

 may be employed. It slides down completely over the 

 object observed, and guards it effectually from all rays of 

 light not transmitted through it, so that it is observed purely 

 as a diaphanous body, and not partially also as an opaque 

 one (as is frequently the case with transparent objects 

 treated in the common way). This piece of apparatus is 

 of much use in verification. 



The stage may, moreover, be removed altogether; and 

 the bar being in the horizontal position, the vase may be 

 placed on a proper support in its stead, and observed 

 from without as well as from within. 



5th. Method of mounting the Diamond and Sapphire 

 Microscopes for Transparent Objects. When the use of 

 the engiscopic part of the instrument is thoroughly 

 attained, nothing can be more easy than the management 

 of these. All that is requisite is to unscrew the body 

 from the arm ; and by detaching the teeth of the wheel 

 from the endless screw, according to the directions already 

 given, to reverse the ends of the arm 9 so that the micro- 

 scope shall come into play; whent he rotatory movement 

 must be again secured, by bringing the endless screw iu 

 contact with the wheel, and clamping it tight : thus the 

 instrument becomes converted into a simple microscope 

 of the first quality, which is to be used exactly as the 



