Eoyal Society. 297 



in April, least in January ! ! The mean of 8 A.M. is 29'620 ; 

 therm. 33'75. The mean of 2 P.M. is 29'631 ; therm. 34'73 ; 

 and at 8 P.M. 29'631 ; therm. 30 0> 57. The diurnal observa- 

 tions assist to support Professor Forbes's theory ; but as in the pre- 

 ceding year, the P.M. observation is at fault; and if the hour had 

 been 9 o'clock instead of 8 o'clock, it would probably have been 

 more so than it appears. The low annual mean state of the baro- 

 meter for the year 1837-38 is even increased in the last year's ob- 

 servations ; and as fresh instruments * appear to have been used, 

 there is ground to believe that the fact is associated with the lo- 

 cality, and it may be desirable not only to record in the Proceed- 

 ings of the Royal Society the data already supplied, but to re- 

 commend to Mr. Thomas more particular inquiry on the subject. 



The phenomena of the Aurora Borealis appear to have been ob- 

 served by Mr. Thomas with great assiduity, and recorded with great 

 care. On examining the register, with reference to M. Erman's 

 important remark, that " in Siberia two kinds of aurora are distin- 

 guished, one having its centre in the west, and the other in the east, 

 the latter being the more brilliant," it is found that twenty-two 

 nights occur in the course of the two winters in which the formation 

 of arches of the aurora is noticed and their direction recorded ; of 

 these, ten are to the west, having their centres rather to the south- 

 ward of west, the arches extending from N.W. to S.S.E. and 

 S.E. ; seven are to the east, or more precisely to the southward of 

 east, the arches extending from N.E. to S.E. and S.W. Of the 

 five others, four are said to be from east to west across the zenith, 

 and cannot therefore be classed with either of the preceding, and 

 one is noticed generally as being to the north. The facts here 

 recorded appear to afford an evidence of the same nature as those 

 mentioned by M. Erman, as far as regards there being two centres 

 of the phenomena. In respect to the relative brilliancy of the east- 

 ern and western aurora, nothing very decided can be inferred from 

 the register. If, as M. Erman supposes, they may be referred 

 respectively to " les deux foyers magnetiques de 1'hemisphere bo- 

 real," it is proper to notice that the position of Alten is nearly mid- 

 way between those localities. 



There can be no doubt that the frequent appearance of the 

 aurora, and the peculiarities of the phenomena observed there, ren- 

 der it a most desirable quarter for a magnetical and meteorological 

 observatory. 



EDWARD SABINE. 

 W. H. SYKES. 



2. " Second Letter on the Electrolysis of Secondary Compounds, 

 addressed to Michael Faraday, Esq., D.C.L., F.R.S., &c." By J. 

 Frederic Daniell, Esq., For. Sec. R.S., Professor of Chemistry in 

 King's College, London. 



The author, in this letter, prosecutes the inquiry he had com- 

 menced in the former one, [of which an abstract appeared in the 



* It appears that the barometer was compared before leaving France, and sub- 

 sequently to its being taken back to that country. 



