ON THE PROGRESS OF SCIENCE. XI 



bear to certain phenomena of terrestrial magnetism, have attracted 

 fresh interest to the study of the solar surface ; and upon the suggestion 

 of Sir John Herschel, a photoheliographic apparatus has lately been es- 

 tablished 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 Wil- 

 liam Herschel accounted for the solar spots by currents of an elastic 

 fluid ascending from the body of the sun, and penetrating the exte- 

 rior luminous envelop. A somewhat different speculation of the same 

 kind has been recently advanced by Mosotti, who has endeavored to 

 connect the Phenomena of the solar spots with those of the red protub- 

 erances which appear to issue from the body of the sun in a total eclipse, 

 and which so much interested astronomers in the remarkable eclipse 

 of 1842. Next to the sun, our own satellite has always claimed the 

 attention of astronomers, while the comparative smallness of its dis- 

 tance 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 in 1852, it was pro- 

 posed that the Earl of Rosse, Dr. Robinson, and Prof. Phillips be re- 

 quested to draw up a Report on the physical character of the moon's 

 surface, as compared with that of the earth. That the attention of 

 these eminent observers has been directed to the subject, may be in- 

 ferred from the communication lately made by Prof. Phillips to the 

 Royal Society on the mountain Cassendi, and the surrounding region. 

 But I am not aware that the subject is yet ripe for a Report. I need 

 not remind you that the moon possesses neither sea nor atmosphere of 

 appreciable extent. Still, as a negative, in such case, is relative only 

 to the capabilities of the instruments employed, the search for the in- 

 dications of a lunar atmosphere has been renewed with fresh augmen- 

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

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

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

 1857, was observed with this reference, and is said to have exhibited 

 no hesitation, or change of form or brightness, such as would be pro- 

 duced by "the refraction or absorption of an atmosphere. As respects 

 the sea, the mode of examination long since suggested by Sir David 

 Brewster is probably the most effective. If water existed on the 

 moon's surface, the sun's light reflected from it should be completely 

 polarized at a certain elongation of the moon from the sun. No traces 

 of such light have been observed ; but I am not aware that the obser- 

 vations have been repeated recently with any of the larger telescopes. 

 It is now well understood that the path of astronomical discovery is 

 obstructed much more by the earth's atmosphere than by the limita- 

 tion of telescopic powers. Impressed with this conviction, the Asso- 

 ciation has, for some time past, urged upon Her Majesty's Government 



