ZOOLOGY AND BOTANY, MIOKOSCOPY, ETC. 



643 



Fig 



Geneva Go's. Reading Microscope. — In this Microscope (fig. 161) 

 designed more particularly for astronomical purposes — the determination of 

 the nadir with a mercury bath — the principle of the 

 " Vertical Illnminator " is made use of for illumination. 



Just below the 1 in. objective is a circular opening 

 which admits light to a piece of thin cover-glass, which 

 is supported on an axis which passes out at one side 

 and terminates in a milled head. On setting the thin 

 glass at the appropriate angle, light is reflected on the 

 object under examination, while at the same time the 

 glass does not obstruct the observer's vision through 

 the eye-piece and objective. The upper milled head 

 clamps the body-tube in the socket when it has been 

 adjusted to the proper focus. The whole instrument 

 is 4 in. high. 



Cambridge Scientific Instrument Co.'s Reading 

 Microscope, — This (fig. 162) is also intended for 

 reading off measurements by the aid of a compound 

 Microscope. The one figured has a single Microscope 

 only, but some are supplied with two. 



The Microscope slides in a socket attached to a 

 frame which moves in a deep Y-shaped groove on the 

 top of a heavy open brass support, A micrometer 

 screw acting against an upper and lower spiral spring 

 moves the Microscope laterally, the extent of movement being indicated on 

 a horizontal graduated bar, the periphery of a coned nut on the screw axis 



Fig. 162. 



serving as the index. Fractions of divisions are recorded by graduations on 

 the nut itself, the bar, which has a bevelled edge, here acting as the index. 

 Campani's Compoiind Microscope. — One of the earliest opticians 

 known to have made a specialty of the construction of Microscopes was 



