341.  It seems just possible that the air which was passing by the kite and string, being in an electrical state sufficient to produce the “usual shocks” only, could still, when the electricity was drawn off below, renew the charge, and so continue the current.  The string was 1500 feet long, and contained two double threads.  But when the enormous quantity which must have been thus collected is considered (371. 376.), the explanation seems very doubtful.  I charged a voltaic battery of twenty pairs of plates four inches square with double coppers very strongly, insulated it, connected its positive extremity with the discharging train (292.), and its negative pole with an apparatus like that of Mr. Barry, communicating by a wire inserted three inches into the wet soil of the ground.  This battery thus arranged produced feeble decomposing effects, as nearly as I could judge answering the description Mr. Barry has given.  Its intensity was, of course, far lower than the electricity of the kite-string, but the supply of quantity from the discharging train was unlimited.  It gave no shocks to compare with the “usual shocks” of a kite-string.

342.  Mr. Barry’s experiment is a very important one to repeat and verify.  If confirmed, it will be, as far as I am aware, the first recorded case of true electro-chemical decomposition of water by common electricity, and it will supply a form of electrical current, which, both in quantity and intensity, is exactly intermediate with those of the common electrical machine and the voltaic pile.

* * * * *

III. Magneto-Electricity.

343. Tension.—­The attractions and repulsions due to the tension of ordinary electricity have been well observed with that evolved by magneto-electric induction.  M. Pixii, by using an apparatus, clever in its construction and powerful in its action[A], was able to obtain great divergence of the gold leaves of an electrometer[B].

  [A] Annales de Chimie, l. p. 322.

  [B] Ibid. li. p 77.

344. In motion:  i. Evolution of Heat.—­The current produced by magneto-electric induction can heat a wire in the manner of ordinary electricity.  At the British Association of Science at Oxford, in June of the present year, I had the pleasure, in conjunction with Mr. Harris, Professor Daniell, Mr. Duncan, and others, of making an experiment, for which the great magnet in the museum, Mr. Harris’s new electrometer (287.), and the magneto-electric coil described in my first paper (34.), were put in requisition.  The latter had been modified in the manner I have elsewhere described[A] so as to produce an electric spark when its contact with the magnet was made or broken.  The terminations of the spiral, adjusted so as to have their contact with each other broken when the spark was to pass, were connected with the wire in the electrometer, and it was found that each time the magnetic contact was made and broken, expansion of the air within the instrument occurred, indicating an increase, at the moment, of the temperature of the wire.