Page:Popular Science Monthly Volume 83.djvu/611

Rh depends upon the ratio of length to cross-section. The second experiments comprised the comparison of the currents flowing through two conductors of equal length and equal cross-section, one of which was of circular and the other of very flat section. The result showed that with the same electromotive-force the currents were also the same, thus proving the current to be uniformly distributed throughout the section. His third series of experiments gave a verification of the laws of parallel resistances. These results constitute a full experimental proof of part II. of Ohm's law, which, in its entirety, had not been given up to this time.

3. Experiments showing the relation between the magnetic effect of the current, the electromotive-force of the cell, and the length of wire in the circuit. This is the relation which we have denominated part I. of Ohm's law. He first presented it in the rather unfamiliar form of the following equation.

where X is the magnetic effect of the current, a and b are constants depending respectively upon the electromotive-force and the internal resistance of the source of current; x is the length of wire constituting the external resistance under test. In modern language equation (4) may be written,