ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



491 



end in a spiral manner. A spring catch indicates when the object is 

 exactly in line of vision. The body of the instrument is fixed at an 

 angle of 45° approximately, this being found the most convenient 

 position for ordinary observation. Illumination is obtained from an 

 adjustable plano-concave mirror mounted in the interior of drum. All 

 parts projecting outside the case are securely protected from injury, and 

 the door is fitted with lever lock. The most suitable powers to use with 

 the instrument are from 2-| in. The instrument is made by Messrs. 

 Watson and Sons. 



Konkoly's Large Measuring Microscope.* — This apparatus (fig. 122) 

 is made by Messrs. Otto Toepfer und Sohn, of Potsdam, and is listed 



Fig. 122. 



No. Sb in their catalogue. The instrument is specially intended for the 

 measurement of sunspots, but is equally well adapted for other purposes. 

 It is built up on a heavy cast-iron base plate, moving on three foot- 

 screws. The upper surface of this base plate is planed, the lower strongly 

 ribbed ; the centre part is perforated for the admission of light on to the 

 plate to be measured. In the front of the base plate there is a prism 



* Otto Toepfer und Sohn's Catalogue (Neue Astrophysikalische Apparate, 

 1908), Potsdam. 



