and on those produced by the Earth's Atmosphere, §c. 389 
those on the other, like the divisions in the vernier and the 
limb of a circle, and their coincidence or uon-coincidence 
became a matter of simple observation. I then superimposed 
the two spectra, when they were both formed by solar light, 
and thus exhibited at once the two series of lines, with all 
their coincidences, and all their apparent deviations from it. 
Professor Airy, to whom J showed this experiment, remarked, 
that he saw the one set of lines through the other, which is 
an accurate description of a phenomenon, perhaps one of the 
most splendid in physical optics, whether we consider it as 
appealing to the eye or to the judgement. 
The general coincidence, thus cognisable by the eye, re- 
quires to be more particularly explained. Though some of 
the larger lines in the gaseous spectrum coincide with some 
of the larger ones in the solar spectrum, yet, In many cases, 
faint and narrow lines in the one coincided with strong and 
broad lines in the other; and there were some strong gaseous 
lines, and even broad hands, to which I could discover no 
counterpart in I’raunhofer’s map of the spectrum, which, at 
this stage of my inquiry, was the standard to which I appealed. 
This discrepancy at first embarrassed me, and, as I observed 
it in parts of the spectrum where Fraunhofer had laid down 
every line which he had seen with his finest instruments, I 
abandoned all hopes of being able to establish the general 
principle of their identity. 1 was therefore obliged either to 
renounce this principle as one contradicted, or rather not con- 
firmed by observation, or to consider Fraunhofer’s delinea- 
tion as in fault, and to enter upon the Herculean task of 
making a better map of the spectrum. 
The magnificence of Fraunhofer’s instruments,—the means 
of nice observation which he had at his command,—and his 
great skill as an observer, were considerations which long de- 
terred me from even attempting to repeat his examination of 
the spectrum. Possessing such inferior means, and situated 
in so unfavourable a climate, I should have felt the attempt 
as presumptuous; but in the comparison which I had already 
made of the gaseous and solar lines, I had detected grave 
errors, and inexplicable omissions, in Fraunhofer’s map, and 
was disposed even to adopt the suggestion of Mr. H. F. Tal- 
bot, (to whom I mentioned the fact, and who had the same 
confidence that f had in Fraunhofer’s accuracy,) that a change 
might have taken place in the light of the sun itself, and that 
the delineation of the Bavarian philosopher might have been 
perfecily accurate at the time when it was executed. This 
supposition, however, became less and less tenable as I pro- 
ceeded in the identification of the two classes of lines; but 
