308 Mr. Take Sone on the Magnetic Susceptibilities 



free from air, and the other in the extreme smallness of the 

 volume susceptibility of gases. In the present research I 

 paid special attention to tbe preparation of pure gases, the 

 removal of the air contained in the generators and purifiers 

 being the constant object of my endeavour. As for the 

 measurement of the magnetic susceptibility, I succeeded in 

 overcoming the difficulty by constructing an apparatus, by 

 means of which I could seal gases in a glass tube at a very 

 high pressure without the least fear of leakage. This 

 apparatus enabled me to use in each case a quantity of gas 

 sufficient for the determination of its magnetic susceptibility 

 and density. A special magnetic balance of high sensibility 

 was constructed for measuring the magnetic force acting on 

 the gas which was sealed in the glass tube and placed in a 

 strong magnetic field. The details of the method and the 

 arrangement of the experiments are given in the following 

 pages. 



§ 2. Method of Measurement. 



The method of measurement is based on the fol lowing 

 principle : — A cylindrical rod made of the material to be 

 tested is vertically suspended between the horizontal pole- 

 pieces of an electromagnet from an arm of a magnetic 

 balance specially constructed, the 

 lower end of the rod being placed in Fig. 1. 



the axial line of the pole-pieces and -i — /\ — 



the upper end in a place where the 



magnetic field is negligibly small. n 



Suppose at first the balance to 

 be in equilibrium, with no mag- \ 

 netic field acting on it, by applying 

 the field the rod is supposed to 

 undergo a slight upward displace- 

 ment 8a, but in equilibrium acted y' 

 on by a force / arising from an 

 inclination of the balance beam. 



Then this force is just equal to the lifting force due to the 

 magnetic field H. The work done by the force is equal to 

 the change of the magnetic energy of the rod, that is 



f8a=^W^8a, 



where S is the cross-section of the rod, k and k are the 

 susceptibilities of the test specimen and the surrounding 

 medium respectively. 



