THE MICROSCOPE, 21 



To the inner tube, b, all the optical apparatus was adapted, the 

 magnifiers, from four to six in number, being screwed to the 

 end of the small tube, i, and the eye-piece, which consisted of 

 two convex lenses, being fitted into the wooden top of the com- 

 pound body, b. A concave mirror, k, was used for reflecting 

 the light, and a drawer, f, in the base, e, served to contain all 

 the magnifiers and other parts of the apparatus. The only 

 adjustment for focus with which this microscope was pro-' 

 vided, was that accomplished by sliding the tube b up and 

 down in the outer tube a, the tube b being marked with 

 lines at h, to denote the distances through which it should 

 be moved for the different magnifying powers. This instru- 

 ment was subsequently much improved in shape, and was 

 made either of brass or silver, and a rack and pinion were 

 used for the adjustment. It was in great demand at one 

 time, and, with its pyramidal case and drawer with apparatus, 

 may even now be frequently seen exposed for sale. This 

 microscope was styled the double reflecting one, and was the 

 first instrument to which the concave mirror was apphed for 

 illuminating transparent objects, the mode of mounting it 

 being similar to that now adopted. 



In the year 1744, we are told by Baker,* — "That the 

 microscopes of Hooke and Marshall having been reduced to a 

 manageable size, improved in their structure, and supplied 

 with an easy way of enlightening objects by a speculum under- 

 neath, and, in many other respects, rendered agreeable to the 

 curious, by Mr. Culpeper and Mr. Scarlet. Some further 

 alterations were, however, wanted to make this instrument of 

 more general use, as I fully experienced in 1743, when 

 examining daily the configurations of saline substances, the 

 legs were continual impediments to my turning about the 

 slips of glass, besides pulling the body of the instrument up 

 and down, was likewise subject to jerks, wliich caused a 

 difficulty in fixing it exactly at the focus : there was also no 

 good contrivance for viewing opaque objects. Complaining 

 of these inconveniences, Mr. Cuff, the optician, applied his 

 thoughts to fashion a microscope in another manner, leaving 

 * Vol. ii., Employment for the Microscope, p. 422. 



