208 PROCEEDINGS OF THE AMERICAN ACADEMY 



strips were connected by a double copper wire with tlie axle. Upon 

 the circumference of the woodeu disk pressed two brushes of sjiring 

 brass, arranged at such a distance apart, one above the other, that they 

 were never simultaneously in contact with a brass strip. Each brush 

 consisted of two pieces of brass 2.2 cm. wide. Across the axle was 

 placed a strip of brass, held always in contact with the axle by two 

 wires attached to the table. One of these wires was connected with 

 one pole of the battery. The other pole was connected with the two 

 magnets, and each brush was connected with one of the magnets. It 

 is obvious that, by this arrangement, rotation of the disk would cause 

 the current to j^ass alternately through each magnet. In the battery 

 circuit was included a tangent galvanometer, to show any alteration 

 in the strength of the current. It was found that the wheel could 

 easily be turned uniformly 100 times a minute. This obviously 

 magnetizes the iron disk 10,400 times a minute in each direction. 

 The molecular arrangement is consequently changed 20,800 times a 

 minute. 



The elevation of temperature in the iron disk was measured by 

 means of a thermo-electric element. A wire of German silver was 

 soldered in the middle of one surface of the disk, and in the middle of 

 the opposite surface was soldered an iron wire. The two wires were 

 connected respectively with the wire from a reflecting galvanometer 

 of six ohms resistance, and with the iron wire of another iron and Ger- 

 man silver junction. The latter junction was placed in a glass tube, 

 packed with asbestos, and maintained at the temperature of the room. 

 The German silver wire of this junction was connected with the re- 

 maining wire of the galvanometer. The larger iron disk was placed 

 perpendicular to the axis of a glass tube, which exactly fitted it ; and 

 the two wires from it were passed through corks in the extremities of 

 the tube. The tube was placed perpendicular to the axes of the mag- 

 nets, with the iron disk horizontal, and in the centre of the field. 

 Several observations were made with the axes of the magnets in 

 line, and with the axes inclined at an angle of about 90'^. The wheel 

 was turned for three minutes, in some cases four. At the end of this 

 time the deflection in the galvanometer was 0.5 to 0.8 cm., and in every 

 case the same deflection was obtained after equal times, whether the 

 axes of the magnets were inclined at an angle of 180° or of 90'^. 



In the preceding experiments the glass tube was pressed against 

 the cores of the magnets ; separated from them only by a sheet of 

 paper. It was thought that the heating of the cores by the rapid 

 magnetization and demagnetization might be communicated to the 



