168 On a new Relation between Heat and Electricity. [Feb. 13, 



II. " On a new Relation between Heat and Electricity." 

 By Frederick Guthrie. Received January 10, 1873. 



(Abstract.) 



It is found that the reaction between an electrified body and a neigh- 

 bouring neutral one, whereby the electricity in the neutral body is induc- 

 tively decomposed and attraction produced, undergoes a modification 

 when the neutral body is considerably heated. 



Under many circumstances it is found that the electrified body is 

 rapidly and completely discharged. The action of discharge is shown to 

 depend mainly upon the following conditions : — (1) the temperature of 

 the discharging body and its distance from the electrified one ; (2) the 

 nature ( + or — ) of the latter's electricity. 



With egard to (1), it is shown that the discharging power of a hot body 

 diniinishes as its distance increases, and increases with its temperature ; 

 but, concerning the temperature, it is proved that the discharging power 

 of a hot body does not depend upon the quantity of heat radiated from 

 it to the electrified body, but chiefly upon its quality. Thus a white-hot 

 platinum wire connected with the earth may exercise an indefinitely 

 greater discharging power, at the same distance, than a large mass of 

 iron at 100° C, though the latter may impart more heat to the electrified 

 body. 



Neither the mere reception of heat, however intense, by the electrified 

 body, unless the latter have such small capacity as to be itself intensely 

 heated, discharges the electricity if the source of heat be distant ; nor is 

 discharge effected when the electrified body and a neighbouring cold one 

 are surrounded by air through which intense heat is passing. But, for 

 the discharge, it is necessary that heat of intensity pass to the electrified 

 body from a neutral body, within inductive range. 



White- and red-hot metallic neutral bodies exercise this discharging 

 power even when isolated from the earth, but always with less facility 

 than when earth-connected. 



The hotter the discharging body, whether isolated or earth-connected, 

 the more nearly ahke do + or — electricities behave in being discharged ; 

 but at certain temperatures distinct differences are noticed. The — 

 electricity, in all cases of difference, is discharged with greater facility 

 than the -}- . 



Attempts are made to measure the critical temperatures at which 

 earth-connected hot iron (1) discharges -+- and — electricity with nearly 

 the same facility, (2) begins, as it cools, to show a preferential power of 

 discharging — , and (3) ceases to discharge — . The temperatures so 

 obtained are measured by the number of heat-units, measured from 0° C, 

 in 1 gram of iron of the respective temperature, represented by the value 

 of the expression Fe %lu. 



