^l^G, — MEASUREMENT OF THOMSON EFFECT IN COPPER. 373 



K X 52.3 X .00714 X 4.2 watts, .00714 being the area of cross section 

 in sq. cm., and 4.2 expressing the relation between calories and watts. 



The resistance of section 4 to 12 is .0025660 ohms, see page 369, col- 

 umn VI. Hence heat is being generated at the rate of 35^ x .0025660 

 = 3.145 watts. 



The rate at which heat is dissipated from section 4 to 12, by radiation 

 and convection = 1.706 watts (see page 369, column X.), if /y, Fig. 3, 

 be taken as the h curve. 



On the assumption that the h curve is straight, heat would be dissipated 

 at the rate of 1.951 watts. 



A small quantity of heat flows into the section at no. 12. It amounts 

 to .1070 watts. 



Collecting the quantities, we have 



^X 4.2 X .00714 X 52.3 = 3.145 + .1070 — 1.706. 



j^ 1.546 ciQ u 



.'. K — = .98 c.g.s. units. 



4.2 X .00714 X 52.3 * 



Taking /i, Fig. 3, as the h curve, we should have K= .83 c.g.s. units. 

 The closeness of these values to the generally accepted ones is a good 

 test of the general accuracy of the work, especially when it is considered 

 that the experiment was not designed with a view to determining the 

 thermal conductivity. 



Experiment with a Heating Current of 30 Amperes. 



This experiment was made on the end of the bar which had not been 

 used in the experiment with 35 amperes, in order to see what effect 

 a considerable change in the important quantities involved in the work 

 would have on the results. 



The data required for the calculation of the value of the Thomson 

 Effect are tabulated on page 375. 



The distribution of temperature along the bar was determined in the 

 same way as before and a very smooth curve obtained, see a e, Fig. 5. 

 The temperatures, column X., page 375, are calculated from the resistances 

 given in columns IV. and VI. 



The change of temperature of the sections on reversal of the heating 

 current is considerably smaller than for the experiment with 35 amperes 

 and the curve cd, Fig. 5, is not as good as the corresponding one in 

 Fig. 3. The curve cd is plotted from the figures in column VIII. The 

 quantities in column IX., from which the change in the rate of heat 

 dissipated is obtained, are taken from the smooth curve. 



