ASTRONOMICAL PHENOMENA AND PROGRESS. 



155 



The comparison of the observations upon the 

 11 -year period in the solar spots, first detected 

 by Schwabe, in 1843, and the corresponding or 

 secular period in the diurnal variation of mag- 

 netic action upon the earth, is still being pros- 

 ecuted ; but no new results of importance are 

 announced. 



Heat of the Sun's Surface, and Currents in 

 its Atmosphere. In a paper before the British 

 Association, Mr. Murphy called attention to 

 the fact ascertained by M. Secchi, of Rome, 

 that the sun's equator is sensibly hotter than 

 its poles. .In accordance with the meteoric 

 theory of the solar heat, this should be the case. 

 The asteroids, or immense meteoric masses 

 which, upon this theory, are supposed to re- 

 volve round and near to the sun, and to fall at 

 successive intervals into its mass, probably oc- 

 cupy like the entire solar system a lenticular 

 space having the greatest diameter nearly 

 coincident with the sun's equator ; and if this 

 be so, a larger number of meteors must fall on 

 the equatorial than on the polar regions of the 

 solar surface, thus making the former more hot. 



The meteoric theory will also account for 

 the currents in the sun's atmosphere, which 

 had been observed by Mr. Carrington. He 

 found that the spots in the lowest latitudes 

 drift most rapidly from west to east. "Were 

 the sun's atmosphere, like the earth's, acted 

 on by no other motive power than the un- 

 equal heating at different latitudes, the rel- 

 ative direction of the currents would be 

 the reverse of this, and in virtue of the well- 

 known principle of trade-winds at the surface 

 of the earth. But if meteors are constantly 

 falling into the sun's mass through its atmos- 

 phere, these bodies moving from west to east 

 with a velocity scarcely less than that of a plan- 

 et at the sun's surface, and if they so pierce 

 the solar atmosphere in greatest number in its 

 equatorial regions, then the result would be a 

 motive power adequate to drive the sun's at- 

 mosphere round it from west to east, and with 

 greatest velocity at the equator. The intensely 

 bright meteoric bodies [see remarks on this 

 phenomenon, September, 1859, in the section 

 above] which Mr. Carrington and another ob- 

 server simultaneously saw traverse the sun's 

 disc, moved from west to east ; and they were 

 almost certainly asteroids falling [or, as Sir 

 "William Armstrong more plausibly suggests,e<m- 

 sequences of the fall of such bodies] into the sun. 



Zodiacal Light. The late lamented Major 

 E. B. Hunt, C. E., U. S. A., communicated to 

 the " American Journal of Science," for May, 

 1863, a paper upon certain astronomical and 

 meteorological phenomena observed by him at 

 Key West, 1857-62. 



He states that during the winter, and es- 

 pecially in February, the Zodiacal Light habitu- 

 ally attains at Key West a remarkable degree 

 of brightness. He repeatedly traced it to the 

 zenith, never with certainty beyond. He was 

 especially interested in certain proofs of the 

 great amount of light proceeding from, the 



source in question. He frequently observed a 

 distinct shadow cast by the Zodiacal Light. This 

 could be seen moving before him when walk- 

 ing from the light on a white roadway, and also 

 upon passing near or waving his arm very close 

 to a whitewashed wall. The shadow was very 

 positive, but (excepting in the last of the cases 

 named) without definite boundaries, as a shadow 

 should be when cast by a light so diffused. 

 This shadow he had observed when the absence 

 of the planet Venus and the total disappearance 

 of twilight refraction forbade its being assign- 

 ed to either of those causes; and other per- 

 sons had corroborated his observations. The 

 principal part of the light appeared to come 

 from the portion within 15 or 20 of the ho- 

 rizon. "It is indeed a singularly beautiful 

 thing, to see this grand mass of mellow light, 

 softly fading out into the clear sky, and quite 

 obscuring the lustre of the Milky Way by its 

 superior brightness. Where it intersects the 

 Milky Way, I think [he concludes] the two 

 are, at the brightest, about equal in glow ; but 

 from thence to the horizon the Zodiacal Light 

 so increases in radiance as to seem almost a 

 prolongation of twilight." 



Mr. Stillman Masterman, of Weld, Maine, 

 also since deceased mentions in the journal 

 already quoted, for July, the fact of his having 

 observed in the Zodiacal Light, on more than 

 one occasion, the appearance of -rapid varia- 

 tions in brightness. These were not wave-like 

 pulsations, like those of the aurora borealis ; 

 but the alternate brightenings and dimmings 

 of the whole area of the light simultaneously. 

 Sometimes there is to be observed a sudden 

 brightening or dimming, without any other 

 change following for a number of minutes. 



In two communications to the " Philos. Mag- 

 azine," February and March, 1863, Prof. Chal- 

 lis gives a theory of the Zodiacal Light. Rea- 

 soning from the observed positions of the light 

 when visible, and the seasons in which it is to 

 be seen, he concludes that the light is simply 

 an immense luminous tract of space, symmet- 

 rically disposed about the sun; its principal 

 plane coincident with the plane of the sun's 

 equator ; its extent in space reaching beyond 

 the radius of the earth's orbit so that, either 

 the earth is at all times enveloped in it, or at 

 least is so when passing across the line of its 

 nodes ; while, as a consequence of their rela- 

 tive positions, this luminous tract will, at cer- 

 tain seasons, especially in low latitudes, be seen 

 as of a conical or pyramidal form, with the 

 base near the sun. The fact of its not being 

 visible in northern latitudes in autumn even- 

 ings and spring mornings, is explained by the 

 small inclination at those seasons of the eclip- 

 tic to the horizon, so that the light fails to pen- 

 etrate the dense parts of the atmosphere then 

 lying between it and the eye. 



Prof. Challis accordingly discards the mete- 

 oric theory of the Zodiacal Light, and considers 

 that it is purely a luminosity of the space it 

 appears in. His theory assumes a universally 



