of material. As yet they had not succeeded in making an iron
accumulator; if they could, they would get about six or seven times
the energy for the same weight of material, or could reduce the
weight proportionately for the same power, and in that way they might
eventually get 70 horse power in a boat of that size, because the weight
of the motor was not great. With regard to the formation of a film on
the surface, no doubt a film of sulphate of lead was formed if the
battery stood idle, but it did not considerably reduce its efficiency;
as soon as it was broke through by the energy being evolved from it, it
would give off its maximum current. They knew by experience that, with
properly constructed accumulators, 80 per cent. of the energy put into
them was returned in work. It was quite certain, as Mr. Crampton said,
that it would be a long time before steam was superseded: he did not
prophesy at all; and he entitled his paper "Electric Launches," because
it would be presumptuous to speak of anything more until larger vessels
had been made and tried.
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