416 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
make room for a glass plate which fits the well of the stage. With the 
instrument come two lenses, 1 in. and 3/4 in., which may be combined 
Fig. 47. 
to secure a 2/3-in. focus. The plan of this Microscope was suggested by 
Prof. J. T. Rothrock, of the University of Pennsylvania, and it is used 
in his botanical classes. 
C2) Eye-pieces and Objectives. 
Apochromatics. — Mr. Edward M. Nelson writes to us: — “In these 
days it becomes an important question whether a given objective contains 
fluorite or not. This can be easily determined by means of the polari- 
scope. Applying this test, I find that in the 24-mm. objective it is the 
middle combination ; in the 12-mm. it is the back, and the combination 
immediately behind the front lens ; in the 1/4 and in Powell’s apochro- 
matic condenser it is the middle and back combinations which have spar 
in them.” 
(3) Illuminating- and other Apparatus. 
Stratton’s Illuminator.* — This lamp is recommended as an addition 
to the paraphernalia of a microscopist. The supporting rods are con- 
* Amer. Mon. Micr. Journ., xiii. (1892) pp. 1-2. 
