4 Prof. Rudberg's Observations on the Magnetic Intensity 



that the observations made at 2 h p.m. are made near the time 

 of maximum, while no observations are made so near the time 

 of minimum temperature. Hence we have 



Observed mean temperature of Irkoutsk . . . 32°*7 Fahr. 



Correction —0 '78 



Corrected mean temperatnre 31*92 



The mean temperature of Irkoutsk is therefore almost ex- 

 actly that of the freezing point. 



As I have no means of ascertaining even the approximate 

 height of Irkoutsk above the level of the sea, it is impossible 

 to compare the above result with that of the formula. I have 

 not, therefore, calculated its distance from the Asiatic Pole ; 

 but taking it rudely from a globe, it is about 27° 10', which 

 by the formula T = (81°*8 sin D') +1°, gives for the tem- 

 perature at the level of the sea 38°\3, leaving a difference from 

 the observed temperature of 6°*4 as due to elevation. 



Irkoutsk is situated in latitude 52° 16'*7 N., and longitude 

 104° 11' E., of Greenwich, according to the observations of 

 Dr. Erman, who at the same time determined the following 

 particulars relative to the magnetic action of the globe. 

 Dip of the North Pole of the needle .... 68° 6' 50 



East declination 2 4 *40 



Magnetic intensity 1*6324 



The following are the results of M. Hansteen's observations 

 made at the same time : 



Dip of the needle 68°12'*9 



Declination 1 37*2 



Magnetic intensity 1 *6466 



II. Observations on the Magnetic Intensity at Paris, Brussels, 

 Gottingen, Berlin, and Stockholm. Extracted from a Letter 

 from Frederick Rudberg, Professor of Physics in the Uni- 

 versity of Upsal, to Sir D. Brewster. 

 HPHE values of the relative magnetic intensity contained in 

 •*■ the following table were obtained, during my journey at 

 the beginning of the present year, from experiments made at 

 Paris, Brussels, Gottingen, Berlin, and Stockholm. The ob- 

 servations were made with an intensity compass, constructed by 

 M. Gambey. To this compass belonged two needles, No. 1. 

 and No. 2, with which I determined, by a particular investi- 

 gation after my return to Stockholm, the variation which the 

 intensity underwent by a change of temperature. The cor- 

 rections which I found were, 



For No. 1. 1 = i (1-0*0004660 /), and 

 For No. 2. i = i (1 -0*0005006 t) 



