289.  M. Colladon, of Geneva, considered that the difference might be due to the use of insufficient quantities of common electricity in all the experiments before made on this head; and in a memoir read to the Academie des Sciences in 1826[A], describes experiments, in which, by the use of a battery, points, and a delicate galvanometer, he succeeded in obtaining deflections, and thus establishing identity in that respect.  MM.  Arago, Ampere, and Savary, are mentioned in the paper as having witnessed a successful repetition of the experiments.  But as no other one has come forward in confirmation, MM.  Arago, Ampere, and Savary, not having themselves published (that I am aware of) their admission of the results, and as some have not been able to obtain them, M. Colladon’s conclusions have been occasionally doubted or denied; and an important point with me was to establish their accuracy, or remove them entirely from the body of received experimental research.  I am happy to say that my results fully confirm those by M. Colladon, and I should have had no occasion to describe them, but that they are essential as proofs of the accuracy of the final and general conclusions I am enabled to draw respecting the magnetic and chemical action of electricity (360. 366. 367. 377. &c.).

  [A] Annales de Chimie, xxxiii. p. 62.

290.  The plate electrical machine I have used is fifty inches in diameter; it has two sets of rubbers; its prime conductor consists of two brass cylinders connected by a third, the whole length being twelve feet, and the surface in contact with air about 1422 square inches.  When in good excitation, one revolution of the plate will give ten or twelve sparks from the conductors, each an inch in length.  Sparks or flashes from ten to fourteen inches in length may easily be drawn from the conductors.  Each turn of the machine, when worked moderately, occupies about 4/5ths of a second.

291.  The electric battery consisted of fifteen equal jars.  They are coated eight inches upwards from the bottom, and are twenty-three inches in circumference, so that each contains one hundred and eighty-four square inches of glass, coated on both sides; this is independent of the bottoms, which are of thicker glass, and contain each about fifty square inches.

292.  A good discharging train was arranged by connecting metallically a sufficiently thick wire with the metallic gas pipes of the house, with the metallic gas pipes belonging to the public gas works of London; and also with the metallic water pipes of London.  It was so effectual in its office as to carry off instantaneously electricity of the feeblest tension, even that of a single voltaic trough, and was essential to many of the experiments.