THE MICROSCOPE. 



13 



carrying at its free extremity a sliding wire, G, to one end 

 of which was attached a pair of forceps, I I, and to the 

 other a small disc of ivory, H, blackened on one side and 

 white on the other; the arm was capable of being adjusted 

 to or from the lens by means of a screw, C, having a nut 

 with a milled head, D ; the spring, E, served to keep the 

 lens holder, A B, in contact with the nut; this form of in- 

 strument is in use at the present day, and a modification of it 

 was adopted by the celebrated Lieberkuhn about forty years 

 afterwards. 



' The wonderful discoveries of Leeuwenhoek made by the 

 single microscope, gave to this kind of instrument an universal 

 reputation, and we find, accordingly, that the compound form 



was laid aside for 

 a time, and the 

 pocket microscope 

 of Mr. Wilson was 

 in great demand. 

 Upwards of thirty 

 years, however, 

 were suffered to 

 elapse before any 

 step was taken (in 

 this country, at 

 least) towards the 

 improvement of 

 this instrument ; 

 the compoimd mi- 

 croscope, then in 

 use, was the con- 

 trivance of Mr. 

 John Marshall, 

 and, from its un- 

 wieldy natiure, was 

 very little em- 

 ployed. It was. 

 Fig. 10. however, the first 



of the compound kind made for sale in England, and is 



