to Reversals of Magnetization in Soft Iron. 209 



Determination of Thermoelectric Constant (April 20, 1888). 



Time. 



Temp, of 

 iron ring. 



Temp, of 



wooden 



ring. 



Difference 

 of tempe- 

 rature. 



Galvanometer- 

 deflexion. 



Difference of 

 temperature 

 corresponding 

 to one division 

 of galvano- 

 meter-deflex- 

 ion. 



0-0811 

 0-0811 

 0-0814 

 0-0816 



h m 

 3 16 



3 47 



4 15 



5 2 



53-4 C. 

 47-9 

 42-9 

 36-3 



16-2 C. 

 16-5 

 16-4 

 16-3 



37-2 0. 

 31-4 

 26-5 

 20-0 



458 

 387| 

 326 

 245 





Mean 



00813 





Hereafter the constant was tested every day by comparing 

 the deflexion of the galvanometer caused by a permanent bar- 

 magnet placed at a definite place. 



The experiment consisted in making three different deter- 

 minations, i. e.: — (1) the strength of the alternating current 

 from which the magnetizing field is calculated ; (2) the rate 

 of alternation per second of time ; (3) the rise of temperature 

 of the junction at the iron ring above that at the wooden ring. 



The alternating current was measured by a deci-ampere 

 balance for small current, and by Siemens's dynamometer for 

 large current. The dynamometer was carefully compared 

 with the ampere-balance, and its constant was *878 ampere per 

 division. The rate of alternation was determined by means of 

 a counter connected to the commutator, and it varied between 

 28 and 400 complete reversals per second. The difference of 

 temperature was observed by the mirror-galvanometer in the 

 thermoelectric circuit. In most cases several observations 

 were made during one experiment, so that the rise of tempera- 

 ture of the iron ring above that of the wooden ring can be 

 graphically represented. Sometimes only the final readings 

 were taken, omitting the intermediate points : these are dis- 

 tinguished from others by simply connecting the final point 

 to the origin by a dotted hue. The figures from 1 to 19 

 represent the experiment. 



From the foregoing description of the method of measuring 

 the difference of temperature, it appears that if the thermal 

 qualities of the two rings are exactly the same, there will be 

 no difference of temperature between the two junctions so long 

 as heat is supplied from the current only, and hence the dif- 

 ference of temperature between the two junctions will indicate 

 the heat due to the reversals of magnetization; in other words, 

 Joule's effect will be entirely eliminated. 



