=Variation of the Experiment.=--When the experiment was varied by substituting a thin iron wire for the stout copper wire at first employed, a very curious result was obtained. The wire chosen was of the same length as the copper, but had a resistance about 1,300 times as great; its resistance being, in fact, 33.3 ohms. Nevertheless, in this experiment, when the B knobs were at a distance of 1.43 inches, no spark passed, which showed that the discharge always followed the line of the conductor, and therefore that the conductor offered less obstruction than 1.43 inches of air. The knobs were then brought gradually nearer and nearer; and it was not until the distance was considerably reduced that the sparks began to pass between them. When the distance was exactly 1.03 inches, the discharge sometimes passed between the knobs, and sometimes through the conductor; this was, therefore, the _critical distance_, in the case of the iron wire. Thus it appeared that the obstruction offered to the discharge by the iron wire was much less than that offered by the copper, the one being equal to a resistance of only 1.03 inches of air, the other to a resistance of 1.43 inches. It does not appear that Professor Lodge undertakes to offer any satisfactory explanation of this result. He has come to the conclusion, from his various experiments, that, in the case of a sudden discharge, difference of conducting power between fairly good conductors is a matter of practically no account; and that difference of sectional area is a matter of only trifling account. But he does not see why a thin iron wire should have a _smaller_ impedance than a much thicker wire of copper. He proposes to repeat the experiments so as to confirm or to modify the result, which for the present seems to him anomalous.[42]