It was mainly owing to the retardation from this cause that communication through the Atlantic cable was so exceedingly slow and difficult.

I will now endeavor to show why the new cable will not be liable to this difficulty, to anything like the same extent.

I have alluded to the resistance offered by the conductor of a telegraph-cable to the passage of an electric current, and to the retardation of this current by static induction.  The terms retardation and resistance are not considered technically synonymous, but are intended, as electrical terms, to designate two very different forces.  The resistance of a wire, as we have seen above, is proportional to its length, and inversely to its diameter.  It is overcome by increasing the number of cells in the battery, or, in other words, by increasing the intensity or force of the current.  The retardation in a telegraphic cable, on the contrary, is proportional to the length of the conducting-wire and the intensity of the battery.  In the former case, by increasing the electrical force you overcome the resistance; while in the latter, by augmenting the electrical force you increase the retardation.

From the foregoing law it will be seen that there are two ways of lessening the resistance upon telegraphic conductors,—­one by reducing the length, and the other by increasing the area of the section of the conducting-wire.  Now, as already remarked, the copper conducting-wire in the old cable weighed but ninety-three pounds to the mile, while in the new cable it weighs five hundred and ten pounds to the mile, or more than five times as much.  If, then, by comparison, we estimate the resistance in the old Atlantic cable to have been equal to two thousand miles of ordinary telegraph-wire, the increased size of the conducting-wire of the new cable reduces the resistance to one-fifth that distance, or four hundred miles.  And while it required two hundred cells of battery to produce intensity sufficient to work over the two thousand miles of resistance in the old cable, it will require but one-fifth as much, or forty cells, to overcome the four hundred miles of resistance in the new cable.  The retardation which resulted from the intense current generated by two hundred cells will be also proportionately reduced in the comparatively small battery of forty cells.  Thus we perceive, that, while the length of the cable is, electrically and practically, reduced to one-fifth of its former length, the retardation of the current is also decreased in the same proportion.  Therefore, if, with the old cable, three words per minute could be transmitted, with the new cable we shall be able to transmit five times as many, or fifteen words per minute.  This is not equal to our Morse system on the land-lines, which will signal at the rate of thirty-five words per minute, still less to the printing system, which can signal at the rate of fifty words per minute; but, even at this rate, the cable would