ark
line of iron in the solar spectrum, numbered 1,474 on Kirchhoff's scale.
But in 1876 Young was able, by the use of greatly increased dispersion,
to resolve the Fraunhofer line "1474" into a pair, the more refrangible
member of which he considered to be the reversal of the green coronal
ray.[521] Scarcely called in question for over twenty years, the
identification nevertheless broke down through the testimony of the
eclipse-photographs of 1898. Sir Norman Lockyer derived from them a
position for the line in question notably higher up in the spectrum than
that previously assigned to it. Instead of 5,317, its true wave-length
proved to be 5,303 ten millionths of a millimetre;[522] nor does it make
any show by absorption in dispersed sunlight. The originating substance,
designated "coronium," of which nothing is known to terrestrial
chemistry, continues luminous[523] at least 300,000 miles above the
sun's surface, and is hence presumably much lighter even than hydrogen.

A further trophy was carried off by American skill[524] sixteen months
after the determination due to it of the distinctive spectrum of the
corona. The eclipse of December 22, 1870, though lasting only two
minutes and ten seconds, drew observers from the New, as well as from
the Old World to the shores of the Mediterranean. Janssen issued from
beleaguered Paris in a balloon, carrying with him the _vital parts_ of a
reflector specially constructed to collect evidence about the corona.
But he reached Oran only to find himself shut behind a cloud-curtain
more impervious than the Prussian lines. Everywhere the sky was more or
less overcast. Lockyer's journey from England to Sicily, and shipwreck
in the _Psyche_, were recompensed with a glimpse of the solar aureola
during _one second and a half_! Three parties stationed at various
heights on Mount Etna saw absolutely nothing. Nevertheless important
information was snatched in despite of the elements.

The prominent event was Young's discovery of the "reversing layer." As
the surviving solar crescent narrowed before the encroaching moon, "the
dark lines of the spectrum," he tells us, "and the spectrum itself,
gradually faded away, until all at once, as suddenly as a bursting
rocket shoots out its stars, the whole field of view was filled with
bright lines more numerous than one could count. The phenomenon was so
sudden, so unexpected, and so wonderfully beautiful, as to force an
involuntary exclamation."[52