ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



703 



slides in the guides at the top of the block. The milled heads at the 

 end of the feet are for levelling the instrument. 



The author claims that the instrument will measure to 1/100,000 

 of a millimetre, and gives a table showing the dimensions of an object 



Fig. 142. 



(at a distance of 1 mm. from the 

 centre of the circle) for angles from 

 4" to 5°. Directions for use are 

 also given, with remarks on the 

 determination of the coefficients of 

 expansion of the metals. 



Double-Drum Microscope- — In 

 this form (fig. 143), the peculiarity 

 is found of two drums, the one 

 serving as the Vjase of the Microscope, 

 and the other as the support of the 



