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HISTOEY OF PHYSICAL ASTEONOMY.

sity of illumination *. Now it is very manifest that the presence of anatmosphere about the sun would occasion a variation in the brightness ofhis disk similar to that above alluded to, since the rays emanating from theedge, by reason of their obliquity, would pass through a greater depth of theelastic fluid, and therefore would undergo a more considerable absorptionthan those proceeding from the regions nearer his centre. Again, it is tobe remarked, that there are not, as in the case of the moon, any facts atvariance with the supposition of an atmosphere about the sun, so extensiveas that which the luminous ring would seem to indicate. Moreover, thehypothesis of a solar atmosphere adapts itself to the modifying phenomenaby which the ring is occasionally characterised, with greater facility thanany other. Thus what can be more natural than the conclusion that thereddish macula observed during the total eclipses of 1733 and 1843were clouds suspended in the solar atmosphere ? These phenomena areso intimately connected with the question relative to the existence of theluminous ring, that it will be desirable to present the reader with adetailed account of the more prominent features by which they were dis-tinguished.

With respect to the spots which appeared during the total eclipse of1733, Vassenius gives the following description of them in a short paperon the eclipse which he transmitted to the Royal Society of London :—“ But what seemed in the highest degree worthy not merely of the admira-tion, but also of the attention of the illustrious Royal Society , w'ere -somereddish spots which appeared in the lunar atmosphere without the peripheryof the moon’s disk, amounting to three or four in number, one of whichwas larger than the others, and occupied a situation about midway be-tween the south and west. These spots seemed in each instance to becomposed of three smaller parts or cloudy patches of unequal length,having a certain degree of obliquity to the periphery of the moon. Havingdirected the attention of my companion to the phenomenon, who had theeyes of a lynx, I drew a sketch of its aspect. But while he, not beingaccustomed to the use of the telescope, was unable to find the moon; Iagain, with great delight, perceived the same spot, or, if you choose, ratherthe invariable cloud occupying its former situation in the atmosphere nearthe moon’s periphery.” He adds, that he continued to observe the phe-nomenon for the space of 40 seconds, until it finally vanished with theappearance of the first rays of the sun f.

Vassenius, in the foregoing account, assumes without hesitation, thatthe luminous ring arises from the existence of a lunar atmosphere. Hisinteresting statement respecting the reddish spots which he perceived init, is corroborated by the pastor of Marstroom, who appears also to havewitnessed a similar phenomenon. The following are the terms in whichCelsius, while citing the observation of Vassenius, alludes to its confirma-tion by that individual:—“ In the luminous ring itself, he (Vassenius)perceived three or four lucid macula of unequal form and magnitudenear the lunar periphery, but still not adhering to it. He also affirms,that at Marstroom, M. Brag, the pastor of the place, also saw the samemacula near the moon’s limb, through an English telescope of excellentconstruction.”];

* Mem. Ast. Soc., vol. xv. p. 11. f Phil. Trans., 1733, p. 135.

j: Acta Lit. et Scien. Suec., vol. iv., p. 65. As it has been considered that the observationof the Swedish pastor, cited in the text, tends to throw some ambiguity (quelque louche)