30 M. A. F. Sundell on the Electromotive and Thermoelectric 



the outer air and that developed by the current in the wires. 

 The positions in which the index becomes stationary are read off 

 a millimetre-scale fixed to the glass tube. The magnitude of the 

 deflection is given by the difference between the numbers read 

 off. A displacement of the liquid one scale- division corresponds 

 to a difference of temperature of o, 002 Cels. 



Each combination was tried with three different intensities of 

 current. From the deflections the quantity a was calculated, 

 which is proportional to the quantity of heat absorbed or produced 

 with the unit of intensity (tan 45°), according to the equation 



as=(\/0?+l)t, ...... (1) 



in which /3 is a constant proportional to the galvanic resistance 

 of the wire in the cylinder, s the current-intensity, and t the 

 deflection. The constant fi is obtained from the deflections / 

 and t x at the intensities s and s 1} by the formula 



R __ (t.S + tsJj^S-tSy) 



The combination of each two of the three current-intensities 

 gave a value of /3 ; in the calculation of a the arithmetic mean 

 of the three values were inserted in equation (1). 



Professor Edlund, in nearly all his experiments, made use of 

 two copper cylinders silvered on the outer side. These cylinders 

 proved now to be no longer air-tight ; and therefore in the pre- 

 sent investigation two others, unsilvered, also employed by Ed- 

 lund in some experiments, were used. 



Waiting till the displacement ceases, before reading-off the 

 position of the column of liquid, makes the labour very tedious. 

 This method is not always practicable, because the index has 

 mostly a motion of its own, independent of the temperature- 

 variation to be measured, the cause of which will be subsequently 

 stated. Professor Edlund therefore made his experiments after 

 the following method. The position of the liquid column was 

 read off at the end of each three quarters of an hour ; and then 

 the current was reversed. The effect of the peculiar motion 

 (which could be taken as uniformly accelerated or retarded) was 

 eliminated in the following manner. The correct deflection, 

 corresponding to the quantity of heat developed or which had 

 vanished at the place of contact, was obtained from three deflec- 

 tions observed in immediate succession, by taking the arithmetic 

 mean of the first and third, and then the mean of this mean and 

 the second deflection. In order to save time, Professor Edlund 

 performed the reading in some experiments every quarter of an 

 hour. Although the temperature of the cylinders had not in so 

 short a time arrived at equilibrium, yet the deflections thus ob- 



