HISTORY OP THE MICROSCOPE. 7 



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 obvious : 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 Leeu- 

 wenhoek's microscopes, which were rendered famous 

 throughout all Europe, on account of the numerous dis- 

 coveries he had made with them. At his death he be- 

 queathed a part of them to the Royal Society. 



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

 a convenient 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 observer, the nature of the object, and the conve- 

 nient examination of its parts required. 



Leeuwenhoek fixed his objects, if they were solid, to these 

 points with glue ; if they were fluid, he fitted them on a 

 little plate of talc, or thin-blown glass, which he afterwards 

 glued to the needle in the same manner as his other 

 objects. The glasses were all exceedingly clear, and of 

 different magnifying powers, proportioned to the nature of 

 the object and the parts designed to be examined. He 

 observed, in his letter to the Royal Society, that " from 

 upwards of forty years' experience, he had found the most 

 considerable discoveries were to be made with glasses of 

 moderate magnifying power, which exhibited the object 

 with the most perfect brightness and distinctness." Each 

 instrument was devoted to one or two objects; hence he 

 had always some hundreds by him. 



The three first compound microscopes that attract our 

 notice are those of Dr. Hooke, Eustachio Divini, and Philip 



