HABTSOEKEB'S MICROSCOPE 



135 



the condenser is better than the plan adopted by Wilson, as it allows 

 the illumination to be focnssed on the object independently of the 

 focal adjustment of the object to the magnifying lens ; whereas in 

 Wilson's microscope, the condenser being mounted in I K, without 

 facility of adjustment, remained at a fixed distance from the object, 

 and hence the control of the illumination was very limited.' 



Another microscope dated 1702 is shown in fig. 103 as drawn by 

 Zahn in his ' Oculus Artificialis.' Fig. 103 presents a back view of 

 it and shows an oval wooden plate ; on the other side of this is a 



similar plate which holds the lens 

 in such a position that it is oppo- 

 site the aperture A. Between the 

 tw r o plates there is a rotary multiple 

 object holder shown in fig. 103A M 

 IS", the object being inserted in the 

 apertures in the circumference of 

 the disc. Focussing is accomplished 



FIG. 103 (1702i. 



FIG. 103A (1686). 



by means of the milled head B which is attached to a screw regulating 

 the distance between the two plates, one of which carries the lens, 

 the other the rotary object holder. The point worthy of note in 

 this instrument is the rotating wheel of graduated diaphragms 

 A, C, I), E, placed on the .^idc away from the lens. This is the first 

 instance of a useful appliance surviving in our present microscopes. 

 In Harris's ' Lexicon Technicum ' (1704, '2 vols. fol.). under the 

 word microscope, Marshall's compound microscope (fig. 104) is 



described and 



figured. 



Several important innovations in micro- 



