48 



THE AMEKICAN MONTHLY 



[March, 



American invention, devised by Dr. 

 J. L. Riddell, of New Orleans. A full 



Fig. 20. 



description of this instrument, with 

 cuts, will be found in Vol. I of this 

 Journal. 



FLINT GLASS 

 PRISM 



Fig. 21. 



The (Abbe binocular eye-piece fig. 

 2o), was fully described in this Jour- 

 nal some time ago (Vol. I, p. 201). 

 A similar arrangement was described 

 by Prof. F. A. P. Barnard, represented 

 in fig. 21. The latter, however, was 

 not an ocular, but was intended to be 

 used in the tube. It differs from 

 Prof. Abbe's device, in having a 

 prism of calcite. 



The Yertical Illuminator. 



[Dr. E. Van Ermengem recently re- 

 counted his experiments with the ver- 

 tical illuminator before the Belgium 

 Microscopical Society. As this in- 

 strument has lately attracted con- 

 siderable attention in this country, as 

 well as abroad, the following summary 

 from the Bulletin des Stances, may 

 prove of interest. — Ed]. 



This apparatus, invented in 1866, 

 by Prof. Hamilton L. Smith, has been 

 for some time used in a manner dif- 

 ferent from that designed by its in- 

 ventor. With the homogeneous-im- 

 mersion objectives it gives results 

 which have arrested the attention of 

 many microscopists, and which have 

 been the object of interesting discus- 



