HISTORY OF THE MICROSCOPE. 



incli long and an inch in diameter, which is provided with a cap at each 

 extremity J the one at a carries a small douhle-convex lens of half an 

 inch in focal length, whilst the one at 6 carries a condensing lens three- 

 quarters of an inch in diameter. 



A vertical section of one of these instruments is seen in fig. 2 : a 

 represents the magnifier, which is lodged in a cavity formed partly by 

 the cap a and by the silver cup or speculum I. In 

 front of the lens is the speculum I, which is a quar- 

 ter of an inch thick at its edge, and whose focus is 

 about half an inch ; in front of this again there is a 

 disk of metal c, three-eighths of an inch in diameter, 

 connected by a wire with the small knob d ; upon 

 this disk the injected object is fastened, and is co- gg. 2. 



vered over with some kind of varnish which has Lieherku/m's 

 dried of a hemispherical figure. Between this knob Microscope. 

 and the inside and outside of the tube there are two slips of thin brass, 

 which act as springs to keep the wire and disk steady. When the 

 knob is moved, the injected object is carried to or from the lens, so as 

 to be in its focus, and to be seen distinctly, whilst the condensing lens 

 6 serves to concentrate the light on the speculum. To the. lower part 

 of the tube a handle of ebony, about three inches in length, is attached 

 by a brass ferrule and two screws. The use of this instrument is ob- 

 vious : it is held in the hand in such a position that the rays of light 

 from a lamp or white cloud may fall on the condenser b, by which they 

 are concentrated on the speculum I ; this, again, further condenses 

 them on the object and the disk c, which object, when so illuminated, 

 can readily be adjusted by the little knob d, so as to be in the focus of 

 the small magnifier at a. 



We must not omit in this place some account of Leeuwenhoek's 

 microscopes, which were rendered famous throughout all Europe, on 

 account of the numerous discoveries he had made with them, as well as 

 from his afterwards bequeathing a part of them to the Koyal Society. 



The microscopes he used were all single, and fitted up in a con- 

 venient and simple manner ; each consisted of a very small double- 

 convex lens, let into a socket between two plates riveted together, and 

 pierced with a small hole ; the object was placed on a silver point or 

 needle, which, by means of screws adapted for that purpose, might be 

 turned about, raised or depressed at pleasure, and thus be brought 

 nearer to, or be removed farther from, the glass, as the eye of the ob- 

 server the nature of the object, and the convenient examination of its 

 parts required. 



