KINQ. — MEASUREMENT OF THOMSON EFFECT IN COPPER. 365 



The relation between temperatures on the air thermometer scale and 

 temperatures by the copper resistance thermometer is expressed by the 

 formula 



The value of S was taken = 1.32. The values of -^ and 8 given here 



were found in some experiments on copper magnet wire made two years 

 ago. A small inaccuracy in the value of these constants is not impor- 

 tant for the work described in this paper; so it was not considered 

 necessary to determine them for the wire actually used. 



The copper resistance thermometer and air thermometer scales agree, 

 of course, at 0° and 100°; but at all other temperatures within the 

 range of work described here there is a slight divergence, perhaps 

 enough to make it worth while to take it into account. 



Experiment with a Heating Current of 35 Amperes. 

 Distribution of Temperature along the Bar. 



This was determined as described on page 360 the resistance of the 

 sections of the bar being measured in terms of the standard S, Fig. 4. 

 (1) With the heating current of 35 amperes. (2) With a current of 

 2 amperes. It was assumed that the current of 2 amperes did not raise 

 the temperature of the bar abovQ that of its surroundings. It will be 

 seen that this assumption is allowable when we consider that 35 amperes 

 heated the bar to a temperature of about 220°, and that the heating is 

 proportional to the square of the current. 



Referring to page 369, column V. gives the observed resistances of the sec- 

 tions of more than half the bar,with acurrent of 2 amperes, and consequently 

 at the temperature of the surrounding water jackets, that is 11°. 9 C. =^ 12°.l 

 Ou. Column VI. gives the observed resistances with the heating current of 

 35 amperes. Column IV. gives ^O' the calculated value of the resistance 

 of each section at 0°. This is found from the resistance at 12°.l Cu, the 



,. i?i2i, . ,, 1 + 12.1 X .00422 ^, TV • .1 



ratio —^ being taken = ■ Column IX. gives the 



temperature of each section calculated by the formula 



^ R-R^ ^ 100 



-^0 :^ _ 1 



^0 



