470 RIESS ON THE INCANDESCENCE OF 
by the discharge; the beads were scattered and melted on their 
surfaces*. Ifa moderate battery discharge is passed through 
a thin strip of tin foil, no visible alteration is produced in it. If 
the strip is attached to a plate of glass and cut through in dif- 
ferent places, and the ends of each piece slightly loosened from 
the glass, then, by a similar discharge, the ends will be lifted up 
and bent back, so that each acquires the form of ac turned on its 
back (© )T. 
The discontinuous discharge artificially produced causes there- 
fore the same effects as were observed above in wires which had 
been submitted to discharges exceeding a certain strength. The 
luminous appearance which accompanies every artificial inter- 
mittent discharge, occurs also, though seldom, when discharges 
are passed through thin wires. Van Marum describes an in- 
stance {, in which an iron wire that was made incandescent by 
a discharge was at the same time surrounded by a brilliant light, 
which appeared to be about an inch in diameter. Here the 
discharge must have taken place at those points where it was in- 
termittent, partly through the substance of the metal and partly 
by spreading itself over its surface. Not only do the striking 
external phenomena of the wire oblige us to assume a naturally 
caused discontinuous discharge, but the less obvious effects in 
the wire are more easily explained by such an assumption. 
It has been shown, that with the first mechanical action upon 
the wire its retarding power was increased; as the discharge 
then becomes intermittent, its transmission through the wire 
must require a longer time. The points of intermittence of the 
discharge are indicated by the bends; the more these increase in 
number the greater is the retarding power of the wires. But at 
the same time this is lessened by the discharge springing from 
place to place, which occurring at so short a distance carries 
forward the discharge more quickly than would happen by a 
continuous discharge; this accounts for the periods in which 
the retarding power remains nearly constant, and for its decrease 
on the splitting to pieces and fusion of the wire. This compen- 
sation of the two opposite actions is illustrated by a case which 
I published on a former occasion §. In the connecting wire of 
* Priestley, History of Electricity, German edition, by Kriinitz, p. 440. 
+ Henry, in Transactions of the American Philosophical Society, vol. vi. 
} Beschreibung einer Elektrisirmaschine, Zweite Fortsetzung, p. 48. 
§ Poggendorft’s Annalen, vol. xliii. p. 78. 
