HISTORY OF PHYSICAL ASTRONOMY.

401

nebulous matter above the luminiferous envelope. Secondly, the ques-tion arises, does any relation subsist between this non-luminous substance,which floats in the upper regions of the solar atmosphere, and either ofthe other two envelopes? Sir John Herschel , in his ingenious theory ofthe physical origin of the solar spots, supposes a perpetual circulation tobe kept up in the solar atmosphere, analogous to that which in the caseof the terrestrial atmosphere produces the phenomenon of the trade winds.Now, is it not reasonable enough to suppose that such a circulation will havethe effect of continually agitating the non-luminous matter constituting theenvelope nearest the solid nucleus of the sun, and throwing up masses ofit above the luminiferous surface ? This view of the subject, while it carrieswith it considerable probability, obviates the necessity of introducing intothe theory of the physical constitution of the sun, the idea of a thirdenvelope independent of the two others. Future observation, prosecutedmore especially with reference to the position of the solar spots duringthe occurrence of eclipses of the sun, can alone be expected to throw anylight upon this interesting question.

Although the physical connexion of the solar spots with the nebulousmatter which appears to exist above the luminous surface of the sun, is apoint which remains to be established definitively by future enquiry, thereis some reason to suppose from the observations of Sig. Santini on theoccasion of the total eclipse of July 8, 184-2, that such a connexion reallysubsists.

In his account of the eclipse, that excellent astronomer states, that afew days previous to its occurrence, he observed a very extensive chain ofspots on the sun, five of which appeared near the western margin of hisdisk. He adds that, although he unfortunately omitted to determinetheir precise position, he felt assured that at the time of the eclipse, theycould not have been very far removed from the singular columns of smokewhich appeared during the total obscuration *.

The aspect presented by the moon during eclipses of the sun, has ledto some curious speculations. Kepler has stated in one of his works, thatduring the obscuration consequent upon a total eclipse of the sun, themoon’s surface is occasionally distinguishable by a rudely light\. A similarappearance has been noticed in modern times during the occurrence ofannular eclipses. Thus Mr. Baily, in his account of the annular eclipseof 1836, states, that “ previous to the formation of the ring, the face of themoon was perfectly black; but on looking at it through the telescope,during the annulus, the circumference was tinged with a reddish purplecolour, which extended over the whole disk, but increased in density ofcolour according to the proximity to the centre, so as to be in that partnearly black.” J

* Giorn. dell’ 1st del Lomb., tom. iv., p. 378. It has been already mentioned that theluminous protuberances seemed to Sig. Santini to resemble irregular columns of smoke,undulating upon broad bases. “ Come irregulari colonne de fuoco ondeggiante a laryabase."

+ Epitome Astronomies, p. 895.

I Mem. Ast. Soc., vol. x., p. 17. Mr. Baily states that at the same time the globularform of the moon was very perceptible; he adds that Mr. Veitch (the gentleman at whoseresidence he observed the eclipse) also noticed the phenomenon, and that both agreed inthe impression that the moon had the aspect of a globe of purple velvet. It is a remark-able fact, that an appearance exactly resembling that described by Mr. Baily was witnessedduring the total eclipse of 1733; thus M. Tissel states, that at Skepshat in Sweden , “themoon’s surface was brighter at the margin near the luminous ring ; towards the middle it