320 Mr. Take Sone on the Magnetic Susceptibilities 



do 2 and d w are the deflexions o£ the scale due to oxygen and 

 water respectively. C is the magnetizing current, S the 

 scale reading, and S the deflexion of the scale. K is a 

 constant which depends on the sensibility of the apparatus 

 and the intensity of the field. 



Fifteen sets of such observations were made at a mean 

 temperature of about 25° 0. ; reducing these observations to 

 20° C. by assuming Curie's law, we obtain the following- 

 result : — 



10 6 . % « = 23*95, 23^52, 24*20, 23*58, 23*58, 24*15, 

 23 69, 24*04, 23-65, 24*37, 23*81, 23*42, 

 24-06, 23*66, and 24-13, 

 the mean value is then 



%a = 23-8 5 xl0- 6 at20°C. 

 with a mean error of +0*07 x 10~ 6 . 



Multiplying the density of air at 20° C. and 760 mm. 

 pressure, we get as the magnetic susceptibility per unit 

 volume of dry air at 20° 0. and at the normal pressure, 

 /^=Q*0237 3 xl0- 6 + 0-00009xl0- 6 . 



§ 6. Oxygen. 



Oxygen is the only gas whose magnetic susceptibility 

 has been determined with a fair accuracy ; yet the values 

 obtained by different observers differ so widely from each 

 other that the extreme values deviate from the mean by 

 more than 10 per cent. 



The following table contains the values which have been 

 determined by several investigators : — 



Table III. 



Date. Observer. k' a . 10 6 . t. 



1853 Faraday* 0143 



1855 Becquerelt 0*149 



1888 Quincke + 0*129 16° 



1888 DuBois§ 0-117 15° 



1893 HennigJ 0*120 25° 



1895 Curie «T 0*115 20° 



1913 Piccard** 0*141 20° 



1916 Booptt 0*146 16° 



* M. Faraday, he. cit. \\ R. Ilemng, loc. cit. 



t E. Becquerel, loc. cit. 51 P- Curie, loc. cit. 



\ G. Quincke, loc. cit. **.* A. Piccard, loc. cit. 



§ H. Du Bois, loc. cit. 



tf W. P. Poop, Phys. Rev. vii. p. 529 (1916). 



In the present experiments the pure oxygen was obtained 



