364 Prof. Draper on inactive Tithonographic Spaces, &c. 
find nothing at all corresponding in magnitude to the great 
lines marked D, E, F, though hundreds of microscopic ones 
may probably exist in these very spaces. 
15. The position of the lines as represented on the sensi- 
tive surface, is found to be, as might have been anticipated, 
independent of the chemical nature of that surface. The 
iodide of silver gives them in the same places as the bromide. 
16. An argument might be drawn, as has been said, from 
the absence of these lines in the yellow and green spaces, as 
to the independence of the dark rays and light. This is, 
however, only another proof of a fact of which we have now 
abundant evidence. In 1834, when my attention was first 
fixed forcibly on these things, and I began to make prismatic 
analyses by the aid of sensitive paper, some of my first trials 
were directed to the detection of these fixed lines. At that 
time I was employing sensitive paper made with the bromide 
of silver, precisely as has been subsequently done in Europe; a 
number of the results were published in the American Journals 
during the year 1837. In the detection of these lines I failed 
entirely, but the bromuretted paper enabled me at that early 
period (whilst the attention of no other chemist was as yet 
turned to these matters) to trace the blackening action from far 
beyond the confines of the violet down. almost to the other 
end of the spectrum. I distinctly made out that the dark rays 
underwent interference after the manner of their luminous 
companions, a result originally due to Arago, and printed some 
long papers in proof of the physical independence of the che- 
mical rays, and light, and heat, throughout the spectrum. 
17. These papers, which I shall probably republish this 
summer, may be found in the Journal of the Franklin Institute 
for 1837. On referring to them, it will be perceived, from the 
great number of remarkable typographical errors, that they 
have been printed from uncorrected proof-sheets. I resided 
at that time a great distance from Philadelphia, in which city 
they were published, and never saw them until long after they 
were in print. 
18. The plates which accompany those papers will show 
that’ the process I then employed was the same as that de- 
scribed in this Journal (December 1842), that is to say, by 
passing the ray through absorbent media and then decom- 
posing it bya prism. Six years have now elapsed since those 
experiments were published. 
