936 THE BELL SYSTEM TECHNICAL JOURNAL, OCTOBER 1951 



is given in Fig. 1. The ordinates are readings of the galvanometer when it 

 was in series with the thermocouples in the moving contact. The circuit for 

 charging the condenser to 40 volts prior to each closure was turned on at 4 

 minutes with the potential of the moving contact positive. The potential 

 was reversed at intervals of If minutes and finally turned off at 15 minutes. 

 The deflections of 43.9 and 55.1 mm occasioned by the energy dissipated 

 at the contact by the discharge of the condenser respectively when the 

 contact was negative and when it was positive are translated into tempera- 

 ture differences of AT = 0.1213 and ^T = 0.1523°C by multiplying by ar^ 

 where a = 3.36 X 10~^ amp/mm of the galvanometer deflection, r = 33.7 

 ohms circuit resistance, and jS = 2.44 X 10^°C/volt thermocouple sensitiv- 

 ity. Neglecting for the moment small corrections due to radiation and con- 

 vection losses, these temperature differences are converted into heat flow 

 along the wire of 22.4 and 28.1 ergs per closure by multiplying them by the 

 factor B = 184.5 obtained from the dimensions of the wire, the thermal con- 

 ductivity of platinum k = 0.699 watt/cm°C, and the factor 60 representing 

 the number of closures per second. 



The heat flow in one of the wires differs from the heat dissipated by the 

 arcs upon that wire because of radiation and convection losses, and because 

 the higher temperature of the positive electrode results in some conduc- 

 tion of heat to the negative electrode at their point of contact. It has been 

 found expedient first to obtain data which are intended to be free from the 

 last of these three sources of error and then to correct for radiation and con- 

 vection losses as obtained by calculation. 



The energy in the electrode wires corresponding to the average excess 

 temperature of the wires above their surroundings (0.07°C) represents the 

 total energy of about 500 arcs. Thus the large scale temperature distribu- 

 tion in one wire is inappreciably changed during the time the wires are in 

 contact after an arc, and the transfer of heat from one to the other can be 

 corrected for by making measurements of Ar across each wire for different 

 fractions x of each cycle during which the wires are in contact and extra- 

 polating the values so obtained to find ATq for zero time of contact. Data 

 of this sort for experimental conditions listed as (1) above are plotted at the 

 lower left side of Fig. 2, and for conditions (3) at the lower right side of the 

 figure; the AT^o values from these curves are written downj on the first line 

 of Table 1. On the upper half of the figure is plotted the total heat flowing 

 along both wires as calculated by multiplying Ar by the factor B = 184.5 

 (not correcting for radiation and convection losses). 



All the solid circles on Fig. 2 (and Fig. 3 also) represent measurements 

 upon the moving electrode, and the open circles measurements upon the 

 stationary electrode. Differences between the solid circles and the open 



