128 Observations and Experiments on Light. 
fect produced by passing a beam of light between extremely minute 
parallel bars arranged in the same plane very close to each other. 
The sun, moon, stars, the flame of a lamp, a small aperture in a 
dark room, &c:, are convenient objects to be examined with the 
eye through the vane of a feather. When we wish to examine 
a luminous object through the vane of a feather, one of a dull or 
dark color should be chosen, as a white feather transmits so much 
light, as soon to exhaust the sensibility of the retina. For form- 
ing colored spectra on a screen a white feather is preferable. 
Those feathers taken from the wing and tail, whose vanes ap- 
proach the nearest to a plane, give the most regular arrangement 
of the spectra. The feathers of small birds, from the greater 
minuteness and delicacy of their structure, produce the most bril- 
liant and extensive colors. We see here the same principle, 
which Dr. Young applied to the construction of the Eriameter.* 
In looking through the vane of a feather at a bright object, the 
most brilliant spectra are seen on the side towards the outer edge 
of the feather. This may be Curia ‘to ‘the meri out * ver 
feather towards the edge. — 
If the above explanation of the shemale of the since be 
correct, it follows, that if an opaque screen be perforated with 
circular holes sufficiently minute and near to each other, it would 
produce’a succession of colored rings. When a beam of light 
passes through a lock of cotton, wool, or raw silk, inflection and 
deflection will take place in every possible direction, producing @ 
blending of all the colors into white light in the centre, and a_ 
succession of colored rings in receding from the centre. Asin 
the feather there is a regular arrangement of the difracting fibres, 
there is a ei tr arrangément of the colored spectra. The 
of the colored rings produced by transmitting a beam 
of. light threagh a lock of cotton, é&c., applies to those produced 
by biierreaeiices-n a pitas ee plate of vue covered wig on 
particles. 
Having satisfied eit with regard to the mucmutave of the 
vane of the feather, and the mode in which it operates in produ- 
cing colored spectra, I concluded, that, if that structure could be 
—_ be — artificial con n , the’ ‘same effects might be 
produced as by the feather. shall not detain the reader ss. 
ie Hes oe 
