154 



THE AMERICAN MONTHLY 

 MICROSCOPICAL APPARATUS. 



[May, 



A Micropolariscope for Projection. — The projection mi- 

 croscojie has long been used to illustrate popular lectures and 

 pai)ers read before microscopical societies. 



The N.J. State Microscopical Society frequently resorts to it, 

 and the writer has been trying for a long time to adapt a polar- 

 iscope to the instrument. On Feb, 25th its performance was 

 shown to the society. A description may be of interest to those 

 who have worked, or who wish to work, on this line. The fig- 

 ure shows how the items of the apparatus are arranged, but 

 does not indicate proportions. 



#:S:;- 



The light comes from an arc lamp provided with an electro- 

 magnet for keeping the crater steadily directed toward the con- 

 denser, the details of which device were p iblished in the Elec- 

 trical Engineer of March 13th. 



The rays diverge from the crater to a plano-convex lens which 

 is one of a pair constituting an ordinary c )ndenser, its mate 

 being shown as recniving parallel rays. Between the first len? 

 and the alum cell is a smaller plano-convex lens of such power 

 as to approximately correct the spherical aberration of the 

 larger lens, so that all rays fall on tjie polarizer at nearly the 

 same angle, namely about 352°. 



