0. N, Rood on Diffraction with the Compound Microscope. 327 
Arr. XXXV.—On a method of exhibiting the Phenomena of 
<4 Api with the Compound Microscope; by Oapen N. 
Roop, A.B. 
[Read before the Berzelian Society of Yale College, March 8.] 
We proceed in the first place to describe a method by which 
any ohe possessing a compound microscope, may, almost without 
other apparatus, repeat in a highly satisfactory manner, all the 
ordinary experiments connected with the subject of diffraction: 
secondly we shall notice one or two of its bearings on micro- 
Scopic vision. 
For observing the phenomena of diffraction, an object lens, the 
half-inch for instance, is to be screwed to the lower end of the 
compound body, and the eye-piece is to be removed: if then the 
inside of the compound body is not well blackened, this must be 
attended to. A convenient way of obtaining a non-reflecting 
surface will be to coil a piece of black paper within the body. 
The instrument thus prepared is to be placed ona table, and a 
beam of sunlight thrown up through the objective by the mirror. 
Atoll of blackened pasteboard eight or ten inches in length, and 
the first reckoning from the centre will be yellow and dark red ; 
the second, blue, yellow, orange, red; the third, blue, green, yel- 
low, ted; the fourth, faint green and faint red. If however the 
rr be larger, (,1,th of an inch,) the eye-piece should be 
ig placed in one end of it, and the other fitting around the com- 
Pound body ; if then an aperture of ;};th of 
Shed card be viewed in this manner, the fringes will be seen, 
wits, may readil be made by placing a piece of sheet-lead on 
Some hard se nlp as a steel plate, and then pressing a fine 
Medle into. the lead. If the aperture be too large for being 
