560 



Mr. A. Stanton. 



surrounding air. A few desultory experiments were made in 

 Dr. Schuster's laboratory, during the hot days of summer about two 

 years ago, as to this discharge when the body was decomposed in the 

 focus of a large concave mirror. The method, depending on excep- 

 tionally brilliant weather, is necessarily inconvenient in this country. 

 Subsequently, during the Long Vacation, I made experiments in the 

 same direction, and tried to use a piece of hot metal for the supply 

 of heat to effect dissociation. These attempts led to an observation 

 of the conditions under which a hot electrified piece of copper or 

 iron could retard a charge of electricity at a good red heat. I 

 observed in my first experiments that if a copper soldering bolt, 

 heated to full redness by a gas blowpipe, was placed on an insulating 

 stand and negatively electrified, discharge took place very rapidly, 

 and occurred so long as the bolt remained visibly red ; that if the 

 bolt was repeatedly heated in an oxidising flame, and electrified, 

 discharge became continuously slower, and that ultimately the copper 

 was capable of retaining a charge perfectly at a full red heat. If 

 the copper bolt, being in the state last described, was allowed to cool 

 completely, the oxide of copper chipped off, and the metal, on heating 

 to redness, behaved generally as at the commencement of the 

 experiments. 



An iron bar was found to behave similarly. 



The experiment was afterwards repeated, with the substitution of 

 a wire kept hot by a current for the massive bar of metal. 



In the later form of the experiment, the hot body was connected 

 to earth, and the discharge of an electrified conductor in the 

 neighbourhood observed. The wire was wound upon a mica frame 

 with thick copper terminals, which served to give the frame 

 rigidity ; the other electrode of the system consisted of a clean flat 

 copper plate, at a distance of 2 or 3 cm. from the frame. The wire 

 used varied from 0*3 to 0"5 mm. in diameter, the length being about 

 60 cm. Both the frame and the flat plate contiguous to it were 

 enclosed in a glass or cylinder surrounded by water to keep it cool, 

 and provided with tubes for the introduction of gases. 



The following are the results obtained ; — 



First, if the conductor contiguous to the wire be positively 

 electrified. 



Here the clean copper wire on becoming red-hot rapidly discharges 

 the conductor ; when a uniform film of oxide is formed, the discharge 



ceases. 



If the containing vessel be now filled with hydrogen, and the wire 

 again heated, a similar discharge takes place until the oxide film is 

 completely reduced; the conductor thereafter retains its charge 

 perfectly. 



Secondly, if the conductor be negatively electrified. 



