capable of emitting; raise them to the same
temperature as the sun itself, and their powers of emission and
absorption being brought exactly to the same level, the thousands of
dusky rays in the solar spectrum will be at once obliterated.

The establishment of the terrestrial science of spectrum analysis was
due, as we have seen, equally to Kirchhoff and Bunsen, but its celestial
application to Kirchhoff alone. He effected this object of the
aspirations, more or less dim, of many other thinkers and workers, by
the union of two separate, though closely related lines of research--the
study of the different kinds of light _emitted_ by various bodies, and
the study of the different kinds of light _absorbed_ by them. The latter
branch appears to have been first entered upon by Dr. Thomas Young in
1803;[389] it was pursued by the younger Herschel,[390] by William Allen
Miller, Brewster, and Gladstone. Brewster indeed made, in 1833,[391] a
formal attempt to found what might be called an inverse system of
analysis with the prism based upon absorption; and his efforts were
repeated, just a quarter of a century later, by Gladstone.[392] But no
general point of view was attained; nor, it may be added, was it by this
path attainable.

Kirchhoff's map of the solar spectrum, drawn to scale with exquisite
accuracy, and printed in three shades of ink to convey the graduated
obscurity of the lines, was published in the Transactions of the Berlin
Academy for 1861 and 1862.[393] Representations of the principal lines
belonging to various elementary bodies formed, as it were, a series of
marginal notes accompanying the great solar scroll, enabling the veriest
tiro in the new science to decipher its meaning at a glance. Where the
dark solar and bright metallic rays agreed in position, it might safely
be inferred that the metal emitting them was a solar constituent; and
such coincidences were numerous. In the case of iron alone, no less than
sixty occurred in one-half of the spectral area, rendering the
chances[394] absolutely overwhelming against mere casual conjunction.
The preparation of this elaborate picture proved so trying to the eyes
that Kirchhoff was compelled by failing vision to resign the latter half
of the task to his pupil Hofmann. The complete map measured nearly eight
feet in length.

The conclusions reached by Kirchhoff were no sooner announced than they
took their place, with scarcely a dissenting voice, among the
esta