132 THE AMERICAN MONTHLY [Ai)ril 



vertical one, the rays being- reflected horizontally by a rig-ht- 

 ang-led prism at the top of the instrument. 



Referring- to the illustration j)ublished in the J(jurnal of 

 May 18, 1895 (p. 154) the g^eneral scheme of arrang-ement 

 is shown. The alum cell is above the second larg-elens as 

 shown, and the sub-stag^e condenser is also removed with 

 the 7-8 objective. The analyser swing's out from the 

 optical axis, as does also a selenite placed where the sub- 

 stag-e condenser is shown. 



As for its performance, the field on the microscope stag-e 

 is 1-4 inch; on the screen, 31 feet distant, it is shown just 

 8 feet in diameter, and as lig-ht as the averag-e field of a 

 calcium lig^ht stereoptican. With polarized lig-ht the struc- 

 ture of g-ranite, pitchstone, Labradorite, and marble were 

 distinctly shown, with the several minerals which were 

 present in them. 



The blue and yellow field obtained by using- the selenite 

 with open and crossed nicols g-ave the effects of polariza- 

 tion with much g-reater distinctness, and added g-reatly to 

 the beauty of the slide. Some of the specimens so showai 

 were chalcedony, salicine, asparag-in, animal and veg-etable 

 sections. If a hair, or any dense tissue was present in the 

 preparation, the exact location of such a part was very 

 clearly shown by this combination of selenite and polari- 

 zer. Thus the stellate hairs of deutzia, the hairs in the 

 nose of a cat, the cartilag-inous portions of a cat's tong-ue, 

 the difference in composition between the nail and the 

 rhizoid processes forming- the "quick;" were all shown far 

 more clearly by this means than by normal lig"ht. The 

 medullary rays in trans-sections of woody stems were 

 also polarized, and indicated a beg-inning- of a new field for 

 the application of this lig-ht, heretofore reg-arded as the 

 monoply of the mineralog-ist and petrolog-ist. 



Dr. A. H. Chester has heartily co-operated with Dr. Van 

 Dyck in his work, and they have used their instrument 

 before the Brooklyn and New York Academies of Science 

 recently and received much encourag-ement and hearty 

 cong-ratulations from other students of physical science. — 

 Frederick H. Blodgett. 



