OP ARTS AND SCIENCES. 115 



The rod of iron or steel, also, when rapidly magnetized and demagnet- 

 ized, gives forth a musical note. 



Owing to the great kindness of Mr. Joseph Wharton, of Philadel- 

 phia, who had provided us with fine specimens of nickel and cobalt bars 

 of his manufacture, and to the courtesy of the officers of the United 

 States Torpedo Station at Newport in allowing us the use of a Wilde's 

 alternating dynamo-electric engine, we were enabled to make the 

 following experiments upon the rapid magnetization and demagnetiza- 

 tion of the magnetic metals, iron, steel, cobalt, and nickel. 



To measure the strength of the current produced by the dynamo- 

 electric machine, we made use of an electrodynamometer similar to 

 that described in Maxwell's " Electricity " which was constructed on the 

 Helmholtz Gaugain princijile both in the fixed and movable coils, and 

 had a resistance of 58.93 of an ohm. The movable coil was suspended 

 from a graduated circle, which read, by means of verniers, to one min- 

 ute. This circle, however, was only used as a check upon the read- 

 ings given by a mirror placed upon the movable coils. The telescope 

 and scale were placed seven feet from the mirror. The electrodyna- 

 mometer was provided with a shunt of one tenth of an ohm, made out 

 of broad ribbons of German silver, the resistance of which did not 

 alter perceptibly during our experiments. Three coarse wire coils of 



resistances 



ABC 



.362 .316 .323 



were provided with glass tubes filled with water, which were carefully 

 placed so as not to conduct heat from the coils surrounding them. 

 The bars of cobalt, nickel, iron, and steel, were all of the same size, 



viz. : — 



length, 15.15 cm. diameter, 1.25 cm. 



Three thermometers, made by Geissler of Bonn, were used, and their 

 readings were subsequently carefully compared with those of a standard 

 Centigrade thermometer, the graduation of which had a probable error 

 of one hundredth of a degree. For this thermometer we were indebted 

 to Professor H. B. Hill, Harvard University. The coils and the ther- 

 mometers were used in alternation ; and the experiments were com- 

 bined so as to give as many experimental equations as were possible in 

 the short time to which the experiments were necessarily limited on 

 account of the rapid heating of the circuit, and also of the rapid rise 

 of temperature of the water in which the magnetic metals were 

 immersed. 



