A change has taken place in the molecules of the wire that is not visible, is noiseless, and that has _traveled along the wire_. It excites neither wonder nor remark. No one asks the reason why. Yet it cannot be explained except by some theory more or less tenable, and the phenomenon, in kind though not in degree, is as unaccountable as anything in the magic of electricity. In a true sense there is, nothing supernatural, or even wonderful, in all the vast universe of law. If we would learn the facts in regard to anything, it must be after we have passed the stage of wonder or of reverence in respect to it. That which was the "Voice of God"--as truly, in a sense, it was and is--until Franklin's day, has since been a concussion of the air, an echo among the clouds, the passage of an electric discharge. It is the first lesson for all those who would understand. The time had now come when that which had seemed a lawless wonder should have its laws investigated, formulated and explained. A man named Coulomb, a Frenchman, is the author of a system of measurements of the electric current, and he it was who discovered that the action of electricity varies, not with the distance, but, like gravity, _in the inverse ratio of the square of the distance_. Coulomb was the maker of the first instrument for measuring a current, which was known as the _torsion balance_. The results of his practical investigations made easier the practical application of electrical power as we now use it, though he foresaw nothing of that application; and the engineer of to-day applies his laws, and those of his fellow scientists, as those which do not fail. Volta was one of these, and he also furnished, as will hereafter be seen, a name for one of the units of electrical measurement.