416 British Association. 



resistance being supposed to bear a sensible proportion to tlie gravitating 

 action. 



The Constitution of the central body of our own system presents a 

 nearer and more interesting subject of speculation. Towards the close of 

 the last century many hypotheses were advanced regarding the nature 

 and constitution of the sun, all of which agreed in considering it an 

 opaque body, surrounded at some distance by a luminous envelope. But 

 the only certain fact which has been added to science in this department 

 is the proof given by Arago that the light of the sun emanated (aot from 

 an incandescent solid, but) from a gaseous atmosphere, the light of incan- 

 descent solid bodies hemg polarized hj refraction, while the light of the 

 sun, and that emitted by gaseous bodies, is unpolarized. According to 

 the observations of Schwabe, which have been continued without inter- 

 mission for more than thirty years, the magnitude of the solar surface ob- 

 scured by spots increases and decreases periodically, the length of the 

 period being 11 years and and 40 days. This remarkable fact, and the 

 relation which it appears to bear to certain phenomena of terrestrial mag- 

 netism, have attracted fresh interest to the study of the solar su?*fece ; 

 and, upon the suggestion of Sir John Herschel, a photoheliographic appa- 

 ratus has lately been established at Kew, for the purpose of depicting the 

 actual macular state of the sun's surface from time to time. It is well 

 known that Sir William Herschel accounted for the solar spots by cur- 

 rents of an elastic fluid ascending from the body of the sun, and penetra- 

 ting the exterior luminous envelope. A somewhat different speculation 

 of the same kind has been recently advanced by Mosotti, who has en- 

 deavored to connect the phenomena of the solar spots witli those of the 

 red protuberances which appear to issue from the body of the sun in a 

 total eclipse, and which so much interested astronomers in the remarka- 

 ble eclipse of 1842. 



Next to the sun, our own satellite has always claimed the attention of 

 astronomers, while the comparative smallness of its distance inspired the 

 hope that some knowledge of its physical structure could be attained with 

 the large instrumental means now available. Accordingly, at the Meeting 

 of the Association held at Belfast in 1852, it was proposed that the Earl 

 of Rosse, Dr. Robinson, and Prof. Phihips be requested to draw up a 

 Report on the pliysical character of the moon's surftice, as compared with 

 that of the earth. That the attention of these eminent observers has 

 been directed to the subject, may be inferred from the communication 

 lately made by Prof. Phillipps to the Royal Society on the mountain 

 Gassendi, and the surrounding region. But I am not aware that the sub- 



ject is yet ripe for a Report. 



mdications of a lunar atmosphere has been renewed with every fresh aug- 

 mentation of telescopic power. Of such indications, the most delicate, 

 perhaps, are those afforded by the occultation of a planet by tlie moon, 

 The occultation of Jupiter, which took place on the 2nd of January last, 

 'sras observed with this reference, and is said to have exhibited no hesita- 



hon, or change of form or brightness, such as would be produced by the 



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