262 Mr. P. Guthrie on a Relation between 



§ 31. Experiment. — The 8-cell battery which I used was not 

 sufficient to heat twelve inches of the wire when in a single loop 

 even to dull redness. Such a non-luminous hot loop discharged 

 an electroscope of — electricity, when at a distance of one inch, in 

 seven or eight seconds. A + charge is not perceptibly affected. 



§ 32. It appears, on comparing the experiments of §§ 1-21 

 with those of §§ 28-31, that the behaviour of red- and w r hite- 

 hot earth-connected iron balls is precisely analogous to the 

 behaviour of red- and white-hot platinum wires heated by gal- 

 vanism. In experiments §§ 28-31 the battery was not in- 

 sulated from the ground. I may mention that repeated and 

 varied attempts by insulating the battery to detect a difference in 

 the discharging-power between an earth-connected and insulated 

 galvanically heated wire (similar to the difference between the 

 discharging-powers of earth-connected and insulated hot iron 

 balls) failed, presumably on account of the considerable amount 

 of neutral matter in the battery, which must be electrically con- 

 nected with the wire. 



§ 33. Experiment. —When the black bottom of a pan of boil- 

 ing water is brought within J inch of the top of an electroscope 

 charged with + or — electricity, ordinary temporary inductive 

 discharge takes place : the leaves recover their divergence com- 

 pletely on the removal of the pan. Yet the actual quantity of 

 heat, as measured by air-expanding power radiated by the bot- 

 tom of the pan upon the electroscope at the distance of | inch, 

 is far greater than that radiated upon it at a distance of 6 inches 

 by the 4-inch long white-hot platinum, wire. This is clearly 

 enough shown by employing the differential air-thermometer 

 with conical copper air-chambers blackened above. The pan 

 has a base about 700 times as great as the orthographic pro- 

 jection of the outline of the spiral, and indefinitely greater 

 than the projection of the wire itself. Immediately the spiral 

 is heated white-hot above one cone, the pan of boiling water 

 (containing an immersed " heater ") is brought so near to the 

 other that the liquid in the bent stem remains for a time sen- 

 sibly at rest. The wire is 6 inches from its cone. The pan 

 has to be placed at a distance of 8 inches to produce equilibrium; 

 and therefore, if the mere quantity of radiant heat received by 

 the electrified body were at all proportional to the amount of 

 discharge, the pan at 8 inches should discharge the electro- 

 scope as rapidly and completely as the white-hot spiral at 6 

 inches. But, as before stated, its permanent discharging-power 

 is practically nothing, even at \ inch. Hence it is clear that the 

 discharging-power depends far more upon the quality of the heat 

 radiated from the discharger, than upon the quantity of heat (as 

 measured in heat-units) received by the electrified body. 



