ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



1049 



thumb-screw passes through the stage near one end, and presses verti- 

 cally against the plates, causing the stage to tilt up at that end ; the 

 fitting of the long screw carrier (angle-piece) is such that the stage at 

 the end is sprung down somewhat forcibly on the brass plates, and it 

 is against this pressure that the focusing screw acts. The metal 

 knob on the object-carrier has a small projection, which appears to 

 have been intended by Leeuwenhoek to fit in the hole in the brass 

 plates beneath it, and thus retain the object opposite the lens. 



It is evident from the extreme simplicity of the construction of 

 this Microscope that the success of Leeuwenhoek' s investigations did 

 not depend essentially on the excellence of the instruments he 

 employed, and as has been before remarked, it is simply wonderful 

 that he was able to do such work with them as is recorded in his 

 publications. 



Musschenbroek's Microscope. — Prof. Hiibrecht also brought with 

 him the Musschenbroek Microscope shown in fig. 217 (about 2/3 size), 

 which is only second in interest to that of Leeuwenhoek. It was 



Fig. 217. 



devised by J. van Musschenbroek (about 1695), the brother of P. van 

 Musschenbroek, who became Professor of Mathematics and Physics at 

 the University of Utrecht. The first representation of this form of 

 instrument was given by Zahn, in his ' Oculus Artificialis,' 2nd ed., 

 1702, p. 781. 



The object-lens is a simple bi-convex lens, mounted between two 

 plates of brass, having minute central apertures forming diaphragms 

 fitting in a horn cell, pierced laterally so as to be adjustable on the 

 end of a metal rod-support, which is connected, by a second rod and 

 three ball-and-socket joints, with a slide-socket in which various 

 object-carriers are placed. The objects were held on the end of a 



