sted; and a quarter of a century
elapsed before a successful "snap-shot" provided photographic evidence
on the subject. It was taken at Novaya Zemlya by Mr. Shackleton, a
member of the late Sir George Baden-Powell's expedition to observe the
eclipse of August 9, 1896;[529] and similar records in abundance were
secured during the Indian eclipse of January 22, 1898,[530] and the
Spanish-American eclipse of May 28, 1900.[531] The result of their
leisurely examination has been to verify the existence of a
"reversing-layer," in the literal sense of the term. It is true that no
single "flash" photograph is an inverted transcript of the Fraunhofer
spectrum. The lines are, indeed, in each case--speaking broadly--the
same; but their relative intensities are widely different. Yet this need
occasion no surprise when we remember that the Fraunhofer spectrum
integrates the absorption of multitudinous strata, various in density
and composition, while only the upper section of the formation comes
within view of the sensitive plates exposed at totalities, the low-lying
vaporous beds being necessarily covered by the moon. The total depth of
this glowing envelope may be estimated at 500 to 600 miles, and its
normal state seems to be one of profound tranquillity, judging from the
imperturbable aspect of the array of dark lines due to its sifting
action upon light.

The last of the five eclipses which we have grouped together for
separate consideration was visible in Southern India and Australia,
December 12, 1871. Some splendid photographs were secured by the English
parties on the Malabar coast, showing, for the first time, the
remarkable branching forms of the coronal emanations; but the most
conspicuous result was Janssen's detection of some of the dark
Fraunhofer lines, long vainly sought in the continuous spectrum of the
corona. Chief among these was the D-line of sodium, the original index,
it might be said, to solar chemistry. No proof could be afforded more
decisive that this faint _echoing back_ of the distinctive notes of the
Fraunhofer spectrum, that the polariscope had spoken the truth in
asserting a large part of the coronal radiance to be reflected sunlight.
But it is usually so drenched in original luminosity, that its special
features are almost obliterated. Janssen's success in seizing them was
due in part to the extreme purity of the air at Sholoor, in the
Neilgherries, where he was stationed; in part to the use of an
i