166 



THE MICROSCOPE : ITS 



highly, and in the fact that the point which carried the object was 



Fig. 29. Fig. 30. 



Leeuwenhoeck's Microscope. 



capable of being raised or lowered by means of a screw or stem. 

 The stem could spring back easily, and, by means of a small screw- 

 nut, the object could be brought nearer to the lens, so as to be 

 perfectly focussed. Leeuwenhoeck had microscopes of differing 

 magnifying power; one is known to have given 270 diameters. 

 The lenses are bi-convex, and very well made. 



The simple microscope was considerably improved by Wilson 

 about 1740. His instrument was furnished with a mirror, and 

 mounted on a stand as shown in Fig. 31. The object was placed 

 between two glass slips, which were held tight between two small 

 brass plates. A tube with a screw thread enabled the object to be 

 raised or lowered so that it could be examined in distinct vision. 

 A spiral spring, pressing from above, holds the plates close, and 

 counteracts, at the same time, the back-lash of the^screw used in 

 focussing. His instrument was in great request, and imitated on 

 all sides. 



