440 RIESS ON THE INCANDESCENCE OF 
give a ribbed, wave-like appearance to the wire. This wave-like 
appearance is also produced by repeated discharges of that quan- 
tity of electricity which causes the wire to become incandescent. 
All the wires hung whilst red-hot in a wide arc; had they 
been suspended from one end and a weight attached to the 
other, instead of bends, merely slight indentations would have 
been observable in them. Hence the remarkable circumstance 
is explained, why, notwithstanding the number of observations 
on the fusion by electricity, the phenomena of bending has only 
been discovered in very recent times. I believe myself to have 
been the first who (in the year 1837) called attention to the 
angular bends in a wire subjected to the electrical discharge*. 
Two years later}, the younger Becquerel makes mention of the 
wave-like bends in very thin platina wires (he could only pro- 
duce them in wires of 0°016 line radius) which had been ex- 
posed several times to a red heat; he however misconceives their 
importance, considering them as the effect of the incandescence, 
and as having no connexion with the shortening of the wires, 
to which we shall now proceed. 
Apparent shortening of the Wires. 
Nairne made the discovery in the year 1780 that wires made 
red-hot by electrical discharges were shortened. An iron wire 
of 0:06 line radius and 10 inches in length, measured only 8°9 
inches after fifteen energetic discharges from a powerful battery 
had been passed through it; it had therefore been shortened one 
inch. The wire retained its original weight, but measured with 
the callipers it appeared to have become thicker. Van Marum 
shortened a wire 18 inches in length and 0°109 line radius a 
quarter of an inch by a single discharge, and assumed, without 
proof§, that the discharge of the electrical current had flattened 
the wire sideways, and that consequently it had become shorter. 
From these few superficial experiments, it was declared uni- 
versally, without hesitation, that metallic wires were expanded 
in thickness, and consequently shortened, by the passage of 
electricity through them||. Even quite recently, the younger 
* Poggendorft’s Annalen, vol. xl. p. 340. 
+ Ann. de Chimie, 2 ser. t, 1xxi. p. 44. Poggendorff’s Ann. vol. xlviii. p. 549. 
+ Philosophical Transactions for 1780, p. 334. 
Beschreibung einer grossen Elektrisirmaschine, erste Fortsetzung. Leipzig, 
1788, p. 13. ap i 
|| Gehler’s Neues Worterbuch, vol. viil.p. 541. Biot, Lehrbuch von Fechner, 
vol. ii. p. 266. 
