ries of progressive
modifications highly interesting in themselves, and full of promise for
the value of the method employed to record them.[546] But experiments on
the subject were singularly interrupted. The volcanic explosion in the
Straits of Sunda in August, 1883, brought to astronomers a peculiarly
unwelcome addition to their difficulties. The magnificent sunglows due
to the diffractive effects on light of the vapours and fine dust flung
in vast volumes into the air, and rapidly diffused all round the globe,
betokened an atmospheric condition of all others the most prejudicial to
delicate researches in the solar vicinity. The filmy coronal forms,
accordingly, which had been hopefully traced on the Tulse Hill plates
ceased to appear there; nor were any substantially better results
obtained by Mr. C. Ray Woods, in the purer air either of the Riffel or
the Cape of Good Hope, during the three ensuing years. Moreover,
attempts to obtain coronal photographs during the partial phases of the
eclipse of August 29, 1886, completely failed. No part of the lunar
globe became visible in relief against circumfluous solar radiance on
any of the plates exposed at Grenada; and what vestiges of "structure"
there were, came out almost better _upon_ the moon than _beside_ her,
thus stamping themselves at once as of atmospheric origin.

That the effect sought is a perfectly possible one is proved by the
distinct appearance of the moon projected on the corona, in photographs
of the partially eclipsed sun in 1858, 1889, and 1890, and very notably
in 1898 and 1900.[547]

In the spring of 1893, Professor Hale[548] attacked the problem of
coronal daylight photography, employing the "double-slit" method so
eminently serviceable for the delineation of prominences.[549] But
neither at Kenwood nor at the summit of Pike's Peak, whither, in the
course of the summer, he removed his apparatus, was any action of the
desired kind secured. Similar ill success attended his and Professor
Ricco's employment, on Mount Etna in July, 1894, of a specially designed
coronagraph. Yet discouragement did not induce despair. The end in view
is indeed too important to be readily abandoned; but it can be reached
only when a more particular acquaintance with the nature of coronal
light than we now possess indicates the appropriate device for giving it
a preferential advantage in self-portraiture. Moreover, the
effectiveness of this device may not improbably be enha