Fiff. 2. 



310 Mr. Take Sone on the Magnetic Susceptibilities 



between the pole-pieces of a Weiss electromagnet, the upper 

 surface of the partition being placed on the axial line of the 

 pole-pieces (fig. 2). The field was then applied and the 

 corresponding deflexion of the 

 scale observed. Since the tube 

 alone produced some deflexion 

 of the scale it was necessary to 

 eliminate the effect by making- 

 two similar observations, first 

 after evacuating the upper half, 

 and secondly after filling it with 

 distilled water. 



If the virtual susceptibility of 

 the system below the glass par- 

 tition be denoted by k ! , we have 

 the following relations for the 

 three cases, when the upper half of the tube is evacuated, 

 and when it is filled with the gas to be tested and with water 

 respectively : 



K — /c'=pS , 

 /e g —/e'=p8 g , 

 K w — K'—ph w , 



where k , te g , and k w denote the susceptibilities of the empty 

 space, the gas, and water respectively, and 6\>, 8 g , and 8 tv are 

 the corresponding deflexions of the scale. 



Eliminating k! from these equations and putting k equal 

 to zero, we get the following relation between the suscepti- 

 bilities of the gas and water : 



8 W — 8 C 



In the actual case, since the glass tube is not placed in a 

 perfectly symmetrical position with respect to the axial line 

 of the pole-pieces, the term k is not zero though it is a 

 small quantity, and it is the susceptibility due to the glass tube 

 itself. In the terms 8„ and S„, the above quantity k due to 



the glass 

 and 8, 



tube is involved, and the differences 8 g 8 = d r/ 



8 Q = d w are the true deflexions due to the glass and 

 water respectively. And finally we get 



K .g __ dg 



•Cm CI m 



If the densities of the gas and water be respectively p g 



