i:',2 THE AMERICAN MONTHLY [A] nil 



vertical oiu-. {hv i"a\>> hcin^' rcllciUMl hoi-i/DiUall \ bv a rifj;-lit- 

 iing"le(l pi-ism at itir toj) dt tlir i nst rii iiuiU. 



Reforrinjr to the illustration piiljlished in the Journal of 

 May IS, 1,S'»S iv. 154) the <>-eneral scheme <»l arrangement 

 is slioun. The alum cell is al)o\e the second laru;e lens as 

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

 the 7-8 olijective. The analyser swings out from the 

 optical axis, as does also a selenite ])laced where the suh- 

 stai);"e condenser is shown. 



As for its performance, the field on the microsco])e sta^^e 

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

 S feet in diameter, and as lijj;"ht as the avera<ife tield of a 

 calcium lisifht stereoj)tican. With {)olarized liy-ht the struc- 

 ture of j^ranite. ])itchstone, Labradorite, and marble were 

 distinctly sliown. with the several minerals which were 

 |)resent in them. 



The blue and vellow tield obtained bv usinj^ the selenite 

 with 0])en and crossed nicols g-ave the effects of polariza- 

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

 the beauty of the slide. Some of the specimens s(^) shown 

 were chalcedony, salicine, asparaj^'in. animal and ve«j;"etable 

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

 ])reparation. the exact location of such a i)art was very 

 clearly shown l)y 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 ton^-ue, 

 the difference in composition between the nail and the 

 rhizoid jirocesses forminj^- the "(juick;" were all shown far 

 more clearh- b\- this means than l)v normal liulU. The 

 medullary ra^'s in trans-sections of woody stems were 

 also polarized, and indicated a l)e<^innin^ of a new held for 

 the application of this li<.iht, heretofore reg"arded as the 

 monoply of the mineraloLrist and petrolofj-jst. 



Ur. A. II. Chester has heartily co-operated with Di". \'an 

 Dyck in his work', and thev ha\e used their instrument 

 before the Brooklyn and New York Academies of Science 

 recently and received much cncoura<j:-ement and hearty 

 cong-ratvdations from other students of ])hysical science. — 

 Frederick If. JUod^j-ftt. 



