Observations and Experiments on Light. 129 
tailing all the expedients which I resorted to in the subsequent 
course of my experiments, but will endeavor to indicate some 
modes of imitating the structure and effects of the vane of the 
feather more perfectly than can be done by any means which are 
at my command, Let it suffice to say, in the mean time, that 
silk cloth of a close and delicate texture, a dense gauze of fine 
wire, and similar contrivances, answer as clumsy substitutes for 
the vane of the feather. 
The difficulty of obtaining the necessary materials, and of 
commanding the requisite mechanical skill, has prevented me 
from executing the most desirable plans, that have presented. 
themselves to my mind. A convenient mode of arranging paral- 
lel fibres is, to bend a steel wire thus, C_____. and wind a fine 
silk thread or delicate wire across its parallel sides. With a con- 
trivance of this kind I was able to produce a row of spectra or 
fringes in a line perpendicular to the parallel fibres. I made use 
of a fine silk thread, but it is manifest, that fibres more minute, 
skilfully arranged, would greatly increase the brilliancy of the. 
phenomena. In this case, it will be seen that the rays undergo 
two difractions in the same’ plane. The second set of fibres 
would increase or diminish the effect of the first set, according as 
its difracting influence coincides with, or counteracts that of the 
first; and it is probable, that both of these effects are produced 
<= different rays. A preferable construction would be to take. 
- metallic frame and wind the finest platinum wire 
across two of its parallel sides, so close as just to admit the pas- 
sage of light between the parallel turns of the wire. The wire 
may be fastened by metallic bars screwed down upon it, where it 
crosses the exterior sides of the frame, and then one set of the 
parallel turns of the wire may be cut away, so as to leave only 
one set to act upon a transmitted beam of light. ‘Two of these 
contrivances might be placed together and turned upon each other, 
so that the parallel wires in one could be made to cross those of 
the other at any convenient angle, and thus the phenomena of 
the feather would be imitated. The crossing of the wires might 
be secured by winding the same frame in opposite directions, fas- 
tening the wires and cutting them away on one side in the man- 
ner above described. ‘The first method, however, is preferable, 
asitadmits the change at pleasure of the angles at which the 
two sets of parallel wires cross each other. This apparatus 
Vol. xx11, No, 1.—Oct.Dec. 1841. 17 
