The experiment referred to is one described in the Philosophical Magazine for July, 1869, p. 9 [Art. 1], where it was shown that, within certain limits, the magnetizing effect of a break-induced current on steel needles is greater the smaller the number of turns of which the secondary circuit consists, the opposite, of course, being true of the effect on a galvanometer. The ground of the distinction is that the galvanometer takes account of the induced transient current as a whole; while the magnetizing-power depends mainly on the magnitude of the current at the first moment of its formation, without regard to the time which it takes to subside.

But even with this explanation, few, I imagine, would be prepared for the result who had not been accustomed to look at electrical phenomena in the light of some dynamical theory. It was for this reason that I considered the matter worthy of experimental investigation, the fruits of which were given in the paper referred to. One point, however, still required a little clearing up; and it is this which I now propose to deal with. I mean the mode of action of the condenser, which was employed, as in the inductorium, for the purpose of rendering the break more sudden, and which I had found necessary for the success of the experiment as then arranged. At this necessity I was not surprised; for, according to the indications of theory, the effect was only to be expected when the fall of the primary current is sudden compared to that of the secondary.