52 HEAT CARRIED OFF BY ELECTRIC CURRENTS. 



like a piece of lime used for reflecting the brilliant 

 calcium light, or like the readily conducting char- 

 coal points, which are not even kindled while used 

 for the radiating arcs of electric light, rivalling 

 sunshine. They serve as electrodes, like the solar 

 orb, passively to receive and transmit electric 

 excitation. A concave mirror similarly receives 

 and reflects the light and heat of sunshine, with 

 sufficient intensity to melt the most refractory 

 metals, while it remains cold. 



The friction of cylinders of electric machines 

 does not heat them, because the action is speedily 

 diffused by the current through the rows of pointed 

 wires arranged opposite to them. In voltaic bat- 

 teries, the liquids do not become hot by the chem- 

 ical action of the acids, the platinum plates and 

 conducting wires serving to transmit the action 

 in closed electric circuits or currents. Neither 

 do the brilliant coruscations of the aurora bore- 

 alis heat the air or earth beneath them. On the 

 contrary, the coruscations of the brilliant electric 

 flashes, and also of lightning from condensing sul- 

 try vapors in the sky, convert the vibrations of heat 

 into electric currents, that quickly carry it off. 



To test the effects produced by the electro- 

 static condition resulting from an equal action of 

 the electric vibrations surrounding a body on all 

 sides, Professor Faraday made an experiment with 

 an insulated metallic chamber, into which, whilst 

 excited by an electrical machine, he entered. He 



