640 PEOCEEDINGS OF THE AMERICAN ACADEMY. 



to H =^ — 35 would make the magnetization of the rod negative while 

 running, but a negative current corresponding to H = — 150 could be 

 used without making the magnetization negative when the current was 

 taken off. A case like this may puzzle the observer if he does not 

 happen to know that the rod he is using — which does not seem to be 



very strongly magnetized — has in fact been exposed to some very in- 

 tense field in the process of manufacture, but this phenomenon is very 

 different from the one which von Walteuhofen describes. 



The Anomalous Magnetization of Short Cylinders. 



The most characteristic examples of really reversed magnetization 

 are to be found, perhaps, among short, stout rods of soft iron and steel, 

 &S, von Waltenhofen and Righi explained many years ago. If such a 

 rod, originally annealed and demagnetized, be placed within a long 

 solenoid and be subjected to a magnetizing field of suitable strength, 

 and if the exciting current be then gradually reduced to zero by the 

 introduction of more and more resistance into the circuit — by very 

 small steps, if not continuously — the remanent magnetism will have 

 the same sign as, but only a small fraction of the strength of, the mag- 

 netization induced in the rod when the current was running. If, how- 

 ever, the current be suddenly interrupted by the opening of the circuit. 



