20 



PRACTICAL TREATISE ON 



At this time, 1740, we find many makers of eminence 

 residing in the metropolis, amongst whom, the names of 

 Cuff, Benjamin Martin, and Adams, require especial notice. 

 Mr. Cuff has already been mentioned as the improver of the 

 solar microscope and of that for opaque objects, both of 

 which were of Lieberkuhn's invention, and we find that in 

 the year 1747 he improved for Martin Folkes the pocket 

 microscope of Wilson, by fixing it to a stand, and by adding 

 a mirror to it; he subsequently improved the stand by 



mounting the lens on a moveable 

 arm, and making the stage to 

 slide up and down on a square 

 stem ; the instrument in this im- 

 proved form was used by EUis in 

 his examinations of coral lines, 

 and a figure and description of 

 the same is given in his work on 

 Zoophytes, published in 1756. 

 The cumbrous compound instru- 

 ment of Mr. Marshall, before 

 described in page 13, was, in 

 1750, improved by Mr. Culpeper, 

 and Mr. Scarlet; they first em- 

 ployed a concave mirror for re- 

 flecting the light through the 

 object and the compound body. 

 Their instrument is represented 

 by fig. 17, it was composed of 

 two tubes, a h, either of wood 

 or paper, sliding one within the 

 other; to the tube a were attached 

 the pillars c d, c d, which rose 

 from the base, e, and supported the 

 round stage, g, in which was a 

 large circular hole for a spring 

 object holder to be fixed, and 

 some smaller holes for the re- 

 ception of the forceps, small condensing lens and fish-pan. 



Fig. 17. 



