271. As heated air discharges common electricity with far greater facility than points, I hoped that voltaic electricity might in this way also be discharged. An apparatus was therefore constructed (Plate III. fig. 46.), in which AB is an insulated glass rod upon which two copper wires, C, D, are fixed firmly; to these wires are soldered two pieces of fine platina wire, the ends of which are brought very close to each other at _e_, but without touching; the copper wire C was connected with the positive pole of a voltaic battery, and the wire D with a decomposing apparatus (312. 316.), from which the communication was completed to the negative pole of the battery. In these experiments only two troughs, or twenty pairs of plates, were used. 272. Whilst in the state described, no decomposition took place at the point _a_, but when the side of a spirit-lamp flame was applied to the two platina extremities at _e_, so as to make them bright red-hot, decomposition occurred; iodine soon appeared at the point _a_, and the transference of electricity through the heated air was established. On raising the temperature of the points _e_ by a blowpipe, the discharge was rendered still more free, and decomposition took place instantly. On removing the source of heat, the current immediately ceased. On putting the ends of the wires very close by the side of and parallel to each other, but not touching, the effects were perhaps more readily obtained than before. On using a larger voltaic battery (270.), they were also more freely obtained. 273. On removing the decomposing apparatus and interposing a galvanometer instead, heating the points _e_ as the needle would swing one way, and removing the heat during the time of its return (302.), feeble deflections were soon obtained: thus also proving the current through heated air; but the instrument used was not so sensible under the circumstances as chemical action. 274. These effects, not hitherto known or expected under this form, are only cases of the discharge which takes place through air between the charcoal terminations of the poles of a powerful battery, when they are gradually separated after contact. Then the passage is through heated air exactly as with common electricity, and Sir H. Davy has recorded that with the original battery of the Royal Institution this discharge passed through a space of at least four inches[A]. In the exhausted receiver the electricity would _strike_ through nearly half an inch of space, and the combined effects of rarefaction and heat were such upon the inclosed air us to enable it to conduct the electricity through a space of six or seven inches. [A] Elements of Chemical Philosophy, p. 153