The agency of galvanism explains why porter has a different and more pleasant taste when drunk out of a pewter-pot than out of glass or earthenware; why works of metal which are soldered together soon tarnish in the place where the metals are joined; and why the copper sheathing of ships, when fastened with iron nails, is soon corroded about the place of contact. In all these cases a galvanic circle is formed which produces the effects. THE SIAMESE TWINS GALVANISED. It will be recollected that the Siamese twins, brought to England in the year 1829, were united by a jointed cartilaginous band. A silver tea spoon being placed on the tongue of one of the twins and a disc of zinc on the tongue of the other, the moment the two metals were brought into contact both the boys exclaimed, “Sour, sour;” thus proving that the galvanic influence passed from the one to the other through the connecting band. MINUTE AND VAST BATTERIES. Dr. Wollaston made a simple apparatus out of a silver thimble, with its top cut off. It was then partially flattened, and a small plate of zinc being introduced into it, the apparatus was immersed in a weak solution of sulphuric acid. With this minute battery, Dr. Wollaston was able to fuse a wire of platinum 1/3000th of an inch in diameter--a degree of tenuity to which no one had ever succeeded in drawing it. Upon the same principle (that of introducing a plate of zinc between two plates of other metals) Mr. Children constructed his immense battery, the zinc plates of which measured six feet by two feet eight inches; each plate of zinc being placed between two of copper, and each triad of plates being enclosed in a separate cell. With this powerful apparatus a wire of platinum, 1/10th of an inch in diameter and upwards of five feet long, was raised to a red heat, visible even in the broad glare of daylight. The great battery at the Royal Institution, with which Sir Humphry Davy discovered the composition of the fixed alkalies, was of immense power. It consisted of 200 separate parts, each composed of ten double plates, and each plate containing thirty-two square inches; the number of double plates being 2000, and the whole surface 128,000 square inches. Mr. Highton, C.E., has made a battery which exposes a surface of only 1/100th part of an inch: it consists of but one cell; it is less than 1/10000th part of a cubic inch, and yet it produces electricity more than enough to overcome all the resistance in the inventor’s brother’s patent Gold-leaf Telegraph, and works the same powerfully. It is, in short, a battery which, although _it will go through the eye of a needle_, will yet work a telegraph well. Mr. Highton had previously constructed a battery in size less than 1/40th of a cubic inch: this battery, he found, would for a month together ring a telegraph-bell ten miles off. ELECTRIC INCANDESCENCE OF CHARCOAL POINTS.