-358 Royal Astronomical Society. 



lavas, craters of tuff*, direction of the fissures of eruption ; and also 

 in the sixth chapter, on trachyte and basaltf, the origin of trap-dikes 

 (p. 123), and the distribution of volcanic vents. The subject of the 

 last chapter we have already stated in detail, and we will here ter- 

 minate this article, commending this " Second Part of the Geology 

 of the Voyage of the Beagle" to the attention of every student of 

 geology and philosophical mineralogy, and hoping that the publica- 

 tion of the Third Part, which will be devoted, we find, exclusively to 

 South America, will follow at no distant period. 



LI I. Proceedings of Learned Societies. 



ROYAL ASTRONOMICAL SOCIETY. 

 [Continued from p. 261.] 

 Dec. 13, r I IHE following communications were read: — 



1844. jL I. Observations of the Moon and Moon-culminating 

 Stars made at Port Essington, on the North Coast of Australia, in 

 longitude 8^^ 48™ 38« east, and latitude 11° 22' south. By Owen 

 Stanley, Esq., Commander R.N. 



The observations give the times of transit of the moon and moon- 

 culminating stars, together with the rates of the clock, and they are 

 corrected for errors of level and azimuth. They extend from June 

 20 to September 22, of the year 1839. No description of the tran- 

 sit instrument, with which they were made, is given. 



II. Announcement of the discovery of Mauvais' Second Comet, 

 in a Letter from M. Mauvais, dated July 9, 1844, addressed to 

 Mr. Baily. 



The comet was discovered on the night of Sunday, July 7, and was 

 observed again on July 8. Information of its discovery was imme- 

 diately forwarded to M. Schumacher. Its positions are given for the 

 times of observation, and the daily motion is deduced from them. 

 The place of the comparison-star is also given. 

 ■ III. Circular Letter from Professor Encke, dated Berlin, 1844, 

 July 10, announcing the independent discovery of the Comet, known 

 as Mauvais' Second Comet, on the night of July 9, by M. D'Arrest, 

 a Student of the University at Berlin. 



* The structure and constitution of the craters of tuff in the Galapagos, 

 as here described, confirm and illustrate what Dr. Daubeny has said (De- 

 scription of Volcanos, p. 180) of the island of Ischia. 



t Mr. Darwin explains, p. 117-124, the facts that trachytic lavas are in 

 general antecedent to basaltic ones, and that in every trachytic district 

 where obsidian has flowed as lava, it has issued from the upper or highest 

 orifices, by supposing that the crystals of felspar which are the principal 

 constituents of trachyte, being of inferior specific gravity to the other ele- 

 ments of (the stony) lavas, but of greater specific gravity than obsidian, have 

 in the former case risen to the upper part of the molten lava, and in the 

 latter sunk to the lower part. He remarks also, that quartz, on the con- 

 trary, would not from its specific gravity tend to sink with the basaltic bases, 

 which would explain the frequent presence and the abundance of that mi- 

 neral in the lavas of the trachytic series. 



