Heat and static Electricity. 261 



forming a circular loop above the cap of the electroscope, and 

 about | inch from it. No effect was produced, whether the elec- 

 troscope was charged with + or — electricity. 



§ 25. Experiment. — A current from eight platin-zinc cells 

 was sent through a flat coil about 20 yards long, intermitting 

 by means of an automatic "make-and-break" of an induction- 

 coil. No effect was produced when the flat coil was within -^ 

 inch of the electroscope charged with + or — electricity. 



§ 26. Experiment. — A secondary flat coil, closed and similar 

 to that of § 25, being placed within y 1 ^ inch of a charged elec- 

 troscope, the intermittent charge was passed through the neigh- 

 bouring primary ; and no effect was produced on an electroscope 

 charged with + or — electricity. 



§ 27. The ground being thus cleared by the experiments of 

 §§ 24, 25, and 26, which show that the passage of a cold gal- 

 vanic current in the neighbourhood of a charged electroscope is 

 without influence, and this being confirmed by the approach and 

 withdrawal of the poles of a powerful permanent magnet, which 

 are also without effect, the action of the heat developed in a pla- 

 tinum wire by means of the current could be studied. 



§ 28. Experiment. — By means of eight platin-zinc cells a 

 platinum wire of # 01 inch diameter and 4 inches long can be 

 raised to whiteness. A -f -charged electroscope is placed an 

 inch below such a coil. About three seconds after the com- 

 pletion of the circuit the platinum wire becomes white-hot ; and 

 by this time the whole of the electricity is discharged. With — 

 electricity the discharge is even more rapid, and is complete 

 even before the wire is white-hot. At a distance of six inches 

 the white-hot platinum-foil discharges both f and — electricity 

 from the electroscope in about seven seconds. If the wire be 

 near its fusing-point, there is little difference either as to dis- 

 tance or time in which the effect is produced with the two kinds 

 of electricity. 



§ 29. Experiment. — Nine inches of the platinum wire of 

 § 28 were bent into a single horizontal circular loop, one inch 

 above the electroscope which was charged with — electricity. 

 The wire was heated to a just visible redness. The electroscope's 

 leaves collapsed in two seconds, one of which is certainly spent 

 in heating the wire, and the other is not more than is required 

 for the fall of the leaves. It appears as though the fall of the 

 leaves were instantaneous. A + -charged electroscope under 

 like conditions requires six or seven seconds to be discharged. 



§ 30. Experiment. — The loop of platinum wire arranged as in 

 § 29 and heated to the same temperature, but placed at a dis- 

 tance of 5 inches above the electroscope, discharges — electricity 

 in two seconds, but requires eight or ten seconds to discharge -f . 



