﻿20 Prof. E. Edlund on the Electromotive Force 



3. The experiments were made in the following manner. 

 After the wire which was to be investigated had been introduced 

 into the copper cylinder and the whole apparatus suitably ar- 

 ranged, the ends of the wire outside the jacket were connected 

 with the poles of five Bunsen's cells. The intensity of the cur- 

 rent was measured with a rheostat. There was moreover in the 

 circuit the usual commutator. To drive part of the air out of 

 the copper cylinder, a more powerful current was used in the 

 first case than that afterwards employed for the proper measure- 

 ments ; thereupon the liquid was poured into the box and the 

 intensity of the current reduced to the magnitude intended for 

 the subsequent experiments. During the cooling the liquid rose 

 in the glass tube; and by raising or lowering the box a suitable 

 position was obtained, which was then permanently adhered to. 

 After the lapse of some time the index remained stationary, and 

 thus showed that the copper cylinder lost just so much heat as 

 was developed by the current in the wire. As in all the ex- 

 periments the temperature of the copper cylinder but very 

 slightly exceeded that of the surrounding air and of the zinc 

 jacket, it may be assumed, without any material error, that its 

 loss of heat is proportional to its excess of temperature. Although 

 this excess of temperature is unknown, we have for it a reli- 

 able relative measure. The index in the glass tube gives the 

 mean temperature of the air in the copper cylinder. That the 

 excess of temperature of the copper cylinder bears to the mean 

 temperature a definite relation, which is independent of the 

 degree of heating, is proved by the experiments themselves. If, 

 as shall immediately be shown, the quantities of heat ,be deter- 

 mined which are produced or absorbed at the place of contact of 

 the two metals by the passage of the current, it will be found 

 that these quantities, as theory presupposes, are proportional to 

 the intensity of the current. This result would not follow from 

 the experiments, unless it could be assumed that the mean tem- 

 perature measured by the index bears a definite relation to the 

 excess of temperature of the copper cylinder. After the index 

 has come to rest it gives thus a relative measure for the quantity 

 of heat which the copper cylinder loses during a given time; and 

 this quantity is equal to that which is produced by the current 

 in the same time. Now we assume that while the current con- 

 tinuously traversed the experimental wire, the index has remained 

 at the scale-division a } or that it has advanced A + « divisions 

 from the place which it assumed before the passage of the cur- 

 rent. The quantities of heat produced by the passage of the 

 current are of two sorts. Owing to the voltaic resistance, a 

 quantity of heat is produced in the entire wire which is propor- 

 tional to the square of the intensity. If the intensity of the current 



