138 Mr. H. F. Biggs on Decrease in the Paramagnetism 



Further, for one particular value o£ the current the throw- 

 was observed when the circuit was broken by the spring- 

 break. The strength of the field at the spot actually occupied 

 by the palladium and coil A is then determined by a 

 comparison between the throws given by coils A and B 

 respectively for the same exciting current when the circuit 

 is broken, the galvanometer being standardized in each case 

 by means of the standard inductor. In fact, if A, B be the 

 total areas, Ha, Hb the values of the magnetic force for 

 the same current, © A , ®b the galvanometer-throws on 

 breaking the circuit, Sa, Sb the throws given by the standard 

 in series with coil A, coil B respectively, we may assume 

 (since none of the quantities differ by more than a few per 



cent, as between A and B) that ^ T ^ K = -^M^A- 



Bi±B <H>B/k':B 



While the magnet was excited, coil A v T as kept in position 



by turning the torsion-head. 



7. Adjustment and Measurement of Balancing Current. 



The current was taken from a storage-cell and adjusted by 

 means of a pair of dial-resistances in series, and when the 

 adjustment was reached the two resistances were varied, 

 their sum being kept constant until the voltage-drop over 

 one of them balanced against a standard cell. 



III. Particulars of the Experiment on Palladium. 



The palladium used was prepared electrolytically by 

 Messrs. Johnson and Matthey. Traces of iron were found 

 in this, but they can hardly have affected the measurements 

 of the effect of hydrogen, though the determinations of the 

 susceptibility of palladium itself are probably too high on 

 this account. The disk of foil weighed *17 gram. 



To control the hydrogen-content of the palladium, the 

 charging was done in a sodium hydrate electrolytic cell in 

 series with a rough hydrogen voltameter. The actual 

 measurement of the gas, however, was made by heating the 

 palladium and pumping off the gas evolved into a tube 

 calibrated for the purpose. 



The observations were planned to answer two questions. Let 

 Mi, M 2 be the magnetic moment in the same field, H of the pal- 

 ladium with different hydrogen-contents v v v 2 cm. 3 at N.T.P.,, 

 and let the (negative) quantity (Mj — M 2 )/H(u 1 — v 2 ) = 'Kv be 

 called the " susceptibility-gradient " due to hydrogen. Then 

 the questions to which an answer was sought are : — (1) Is- 



