he article in the _Reader_, partly
reproduced above, and speaks of me as having been replied to in a
previous note. Again in the _Comptes Rendus_ for 1872, Vol. LXXV., p.
1664, he recognizes the inadequacy of his hypothesis, saying:--"Il est
certain que l'objection de M. Spencer, reproduit et developpee par M.
Kirchoff, est fondee jusqu'a un certain point; l'interieur des taches,
si ce sont des lacunes dans la photosphere, doit etre froid
relativement.... Il est donc impossible qu'elles proviennent d'eruptions
ascendantes." He then proceeds to set forth the hypothesis that the
spots are caused by the precipitation of vapour in the interiors of
cyclones. But though, as above shown, he refers to the objection made in
the foregoing essay to his original hypothesis, and recognizes its
cogency, he does not say that the hypothesis which he thereupon
substitutes is also to be found in the foregoing essay. Nor does he
intimate this in the elaborate paper on the subject read before the
French Association for the Advancement of Science, and published in the
_Revue Scientifique_ for the 24th March 1883. The result is that the
hypothesis is now currently ascribed to him.[26]

About four months before I had to revise this essay on "The Constitution
of the Sun," while staying near Pewsey, in Wiltshire, I was fortunate
enough to witness a phenomenon which furnished, by analogy, a
verification of the above hypothesis, and served more especially to
elucidate one of the traits of solar spots, otherwise difficult to
understand. It was at the close of August, when there had been a spell
of very hot weather. A slight current of air from the West, moving along
the line of the valley, had persisted through the day, which, up to 5
o'clock, had been cloudless, and, with the exception now to be named,
remained cloudless. The exception was furnished by a strange-looking
cloud almost directly overhead. Its central part was comparatively dense
and structureless. Its peripheral part, or to speak strictly, the
two-thirds of it which were nearest and most clearly visible, consisted
of _converging streaks_ of comparatively thin cloud. Possibly the third
part on the remoter side was similarly constituted; but this I could not
see. It did not occur to me at the time to think about its cause,
though, had the question been raised, I should doubtless have concluded
that as the sky still remained cloudless everywhere else, this
precipitated mass of vapour mu