ZOOLOGY AND BOTAKY, MICROSCOPY, ETC. 



1 05 



threads, and has two divided circles : one graduated to every ten degrees 

 (for reading off the rotations of the fixed cross-threads) : and a finer one 

 graduated in degrees with a vernier. The prism has right-angled end 

 planes and provides a field of the largest possible size. The instrument 

 can be fitted, if desired, with a long glass tube provided with quadrant 

 Bertrand's quartz plates for sugar analysis. 



Fir.. 20. 



Fig. 27. 



Abbe Drawing 'Camera. — This form of Abbe camera, made by 

 Messrs. Zeiss (fig. 28), was designed by Dr. H. W. Heinsius (1889), 

 and was descrihed in this Journal (1890), p. 94, but was not figured. It 



differs from the one figured in the Journal (1884, p. 119, fig. 18), inas- 

 much as it is attached by a hinge to the collar which fixes it to the 

 Microscope. This permits it to be turned out of the way when it is not 



in use. 



