ASTRONOMICAL PHENOMENA AND PKOGKESS. 



connection between the variation of mean tempera- 

 ture and the appearance of solar spots is indirect 

 rather than direct, that each results from some gen- 

 eral change of solar energy * * * The problems of 

 meteorology appear to be presented here in a sim- 

 pler form than m England, and probably systematic 

 photographic self-registering observations extended 

 over a few years might lead to important results. 



Mr. Francis H. Smith, writing to the Ameri- 

 can Journal of Science, states that, on the 14th 

 of April, at the University of Virginia, he saw, 

 with the naked eye, a large sun-spot just above 

 and to the left of the centre of the sun's disk. 

 The time was shortly before sunset, and, the 

 atmosphere being quite hazy, he could gaze 

 with impunity at the sun, which appeared of a 

 bright-orange color. As thin horizontal streaks 

 of darker haze passed over the disk, the spot 

 came out with remarkable distinctness. Prof. 

 Peters, who was with him at the time, saw it 

 plainly. On a subsequent evening, Mr. Smith, 

 with another observer, obtained a good view 

 of the spot under the ,same circumstances of 

 position, haze, and color. It had moved, how- 

 ever, in the interval, to the right of the sun's 

 centre. He had tried in vain, earlier in the 

 day, to see it through colored glasses. Some 

 time after the first occasion mentioned, he ex- 

 amined the sun with a small refracting tele- 

 scope, and thought there appeared near the 

 indicated position a large spot, with a smaller 

 companion, yet, in the absence of micrometric 

 measurement, he would not have thought it 

 large enough to be visible to the naked eye. 



Auroral Theory of the Sun's Corona. Prof. 

 W. A. Norton contributes a second paper on 

 this subject to the American Journal of Sci- 

 ence, in which he fully discusses his theory, 

 sustaining it principally by the results of ob- 

 servations made at the total eclipse of August 

 7, 1869, when the corona was most successfully 

 studied. In a word, he conceives the sun to 

 be surrounded by a permanent atmosphere, 

 like the earth, and that the corona is nothing 

 but a congeries of auroral streamers shooting 

 out far beyond that atmosphere, similar to 

 those which at times radiate many hundreds 

 of miles into space from the upper atmosphere 

 of the earth. Among the deductions from this 

 theory is this important one : that a portion 

 of the auroral matter from the sun may fall 

 upon the earth's atmosphere, and furnish the 

 substance of terrestrial auroras, for which no 

 terrestrial origin has yet been detected. The 

 zodiacal light Prof. Norton regards as only 

 an indefinite extension of the corona. To the 

 accumulation of solar auroral matter in our at- 

 mosphere, he is led to ascribe the periodic and 

 irregular disturbances of the earth's magnetic 

 condition these disturbances being known to 

 coincide with the increase of sun-spots, which, 

 upon his theory, cause the auroral develop- 

 ments. To his paper, the author adds the fol- 

 lowing interesting note by way of disposing 

 of various theories which do not connect the 

 corona directly with the sun : 

 Some persons have conjectured that the oorona 



might be produced by the passage of the sun's rays 

 through the earth's atmosphere, but it may readily 

 be shown that this is impossible. When one re- 

 flects that the half width of the moon's shadow, in. 

 the larger eclipses, is as great as the estimated height 

 of the atmosphere, it will" be seen that, to an observer 

 on the central line of the eclipse, the line of sight will 

 not fall upon the illuminated portion of the atmos- 

 phere exterior to the shadow, unless inclined under 

 a large angle to the line of direction of the centres 

 of the sun and moon. ^ The corona, therefore, if 

 of terrestrial atmospheric origin, ought to present, 

 toward the middle of the eclipse, the appearance of 

 a halo entirely detached from the dark body of the 

 moon, and many degrees distant from it. It ought, 

 also, to increase in brightness from its inner border, 

 for a considerable distance outward. 

 Others have imagined that the corona might be 



a lunar atmosphere ; but, since some of the stream- 

 ers, or rays of the corona, have been seen to extend 

 to a distance greater than the sun's diameter, this 

 would require the lunar atmosphere to be of vast ex- 

 tent ; whereas, no decisive evidence has yet been ob- 

 tained of the existence of any lunar atmosphere ca- 

 pable of producing a sensible refraction, or reflecting 

 a perceptible amount of the sun's light to an observer 

 on the earth. 



Perhaps the more prevalent idea, at the present 

 day, is, that the corona, with its rays and tufts of light, 

 is a phenomenon of diffraction produced by the pas- 

 sage of the sun's rays along the denticulated edge of 

 the moon. This theory has an air of plausibility, 

 but it is entirely inadequate to account for the great 

 extent of the coronal rays. The fringes produced by 

 the diffraction of light in its passage near the edge 

 of a body appear to the eye of the observer to extend 

 but a small angular distance from the edge. This 

 would be more strikingly true in the case of a distant 

 body, like the moon. 



The only remaining supposition is that the corona 

 is either an envelope of some kind permanently con- 

 nected with the sun, or is made up of material emana- 

 tions proceeding immediately from the sun. To the 

 large body of indirect evidence, that the corona is 

 wholly a solar phenomenon, that has been obtained, 

 we may now add that of direct observation, since it 

 appears that " an examination of the photographs of 

 totality," obtained at the eclipse of 1869, shows that 

 as the moon advanced the corona was progressively 

 covered. 



Eclipse Photographs. Mr. A. Brothers, of 

 London, sends to Nature a note, with an illus- 

 tration, descriptive of the results of his attempt 

 to photograph the eclipse of December, 1870, 

 at Syracuse. He says : 



It will be noticed that there is more of the corona 

 shown on the west side of the moon than on the east, 

 north, or south. This feature is shown on all the 

 plates, so that there can be no question that there 

 was more coronal light on the west side of the moon 

 than at the other points. In explanation of the great 

 display of the outer rays (I use the term rays for 

 want of a better perhaps outer light would be more 

 correct, for there is no indication of lines or rays on 

 any of the plates), I had supposed that the east side 

 might have been partially covered with cloud ; but 

 in conversation with Prof. Eastman I found that he 

 was observing for the reappearance of the sun, and 

 he was quite certain that there was no cloud at the 

 time the photograph was taken that is, at about 

 thirteen seconds from the end of totality. Mr. Fryer 

 also is equally certain that there was no cloud. The 

 plate was exposed^eight seconds. It will be noticed 

 also that the prominences are more numerous on the 

 side where the corona is brightest. 



Various opinions have been expressed as to the 

 quality of the light of the corona. The effect we saw 



