1904.] Thermoelectric Power 'produced by Magnetisation. 423 



was begun, R was adjusted until the galvanometer T showed no 

 deflection when the circuit was closed, though a small permanent 



VVWVW\AAAA\AAA/V — , 

 R 



-4 



Fig. 2. 



current was really of no consequence. The deflection (or increase of 

 deflection), which occurred when M was magnetised was thus entirely 

 due to the change of thermoelectric force by magnetisation. 



The aperiodic galvanometer T, which was placed at a distance of 

 3*5 metres from the magnetising coil, is of the form designed by Ayrton 

 <and Mather ; the resistance of its moving coil together with the 

 suspension is 4°70 ohm. In most of the experiments the distance 

 between the mirror and the scale was 12 feet (3*66 metres), when the 

 deflection for 1 microampere was found to be 54 scale divisions of 

 ^th inch (0-0645 cm.). 



Two magnetising coils were used ; one is 11 - 5 cm. in length and 

 contains 876 turns of No. 18 wire, the field near the middle of its 

 interior due to 1 ampere being 92 units. The length of the other is 

 20'4 cm., and the number of turns of wire 2,770 ; 1 ampere produces 

 a, field of 174 units in its interior. The magnetising current was 

 derived from a battery of 27 storage cells and was measured by a 

 moving-coil ammeter, reading from — 15 amperes by tenths. The 

 ammeter was calibrated by comparison with a tangent galvanometer, 

 and the readings were found to be sufficiently accurate for the purpose 

 in view. Currents of more than 15 amperes were measured by the 

 engine-room ammeter ■ but on account of their excessive heating effect 

 .such strong currents were used in only a few of the experiments. 



The Experiments. 



Iron. — The results of experiments with two different samples of 

 iron and one of steel are shown by curves (A), (B) and (C) in fig. 3, 

 where the ordinates are proportional to the temporary increase of 



