_=178. Condensation; Condensers.=_ As I T easily held more sparks than it would take before (Exp. 70), we say that its _capacity_ has been increased. Its potential didn't increase, because that could not get greater than the potential of E C, the charging body. To describe this state of affairs, we say that the electrification was denser than before, and that it was _condensed_. The _capacity of I T was greatly increased by the presence of another conductor, F B, insulated from I T, but "grounded_." Such a combination, 2 conductors, with a dielectric between them, is called a condenser. A condenser can hold much more electrification at a certain potential than an equal amount of surface can hold when not properly arranged. We might call a condenser a storage battery for static electricity. The capacity of a condenser depends, among other things, upon the area of the conducting surfaces, and upon the thickness and nature of the dielectric. Among the various forms of condensers may be mentioned the Leyden jar, and the fulminating pane. =179. The Leyden Jar= consists of a wide-mouthed glass jar, with tin-foil pasted upon the inside and outside to within 2 or 3 inches of the top. The inner coat or conductor is connected to a knob or ball at the top by means of a chain. To charge the jar, the outer coat is connected with the earth by holding it in the hand, or by resting it upon a table while the electrification is passed to the knob. A _Leyden Battery_ consists of 2 or more connected jars, the object being to increase the area of the surface. The jar is discharged by touching one end of a _discharger_ (§ 188) to the outer coat, and swinging its other end over to the knob, when a bright spark will pass between the knob and discharger. (See Exp. 86.) =180. Fulminating Panes=, or Franklin's Plates, are practically the same as a Leyden Jar. The tin-foil, however, is pasted upon the opposite sides of a pane of glass, a margin of about an inch being left all around. One side of the pane is charged, and takes the place of the inside coat of the jar. The other side is grounded. The pane is discharged by connecting the two sheets of foil. =181. Induction Coil Condensers= consist of sheets of tin-foil separated by sheets of paraffined paper, which act as the dielectric. (See Induction Coils.) =182. Submarine Cables=, with the surrounding water, act like condensers, the result being that the condensing effect slows up the electric current and retards the signals. These make a condenser of enormous capacity. The wires inside form one conductor, and the water the other, while the insulation around the wires forms the dielectric. =EXPERIMENT 84. To study the condensation of electrification.=