PRESIDENTIAL ADDRESS. 615 
power to 8,000 horse-power, are in commercial use. One may well ask: What 
has wrought this astonishing revolution in the face of the unanimous verdict of 
the engineers of 1857 ? 
The answer may be given in terms of the action and reaction of pure and 
applied science. Pure science furnished a discovery; industrial applications 
forced its development; that development demanded further abstract investiga- 
tion, which in turn brought about new applications. It was beyond all question 
the development of the dynamo for the purposes of electrotyping and electric 
light which brought about the commercial advent of the electric motor. For about 
that very time Holmes and Siemens and Wilde and Wheatstone were at work 
developing Faraday’s magneto-electric apparatus into an apparatus of more prac- 
tical shape ; and the electric lighthouse lamp was becoming a reality which Faraday 
lived to see before his death in 1867. That eventful year witnessed the intro- 
duction of the more powerful type of generator which excited its own magnets. 
And even before that date a young Italian had made a pronouncement which, 
though it was lost sight of for a time, was none the less of importance. Antonio 
Pacinotti in 1864 described a machine of his own devising, having a specially 
wound revolving ring-magnet placed between the poles of a stationary magnet, 
which, while it would serve as an admirable generator of electric currents if 
mechanically driven, would also serve as an excellent electric motor if supplied 
with electric currents from a battery. He thereupon laid down the principle of 
reversibility of action, a principle more or less dimly foreseen by others, but 
never before so clearly enunciated as by him. And so it turned out in the years 
from 1860 to 1880, when the commercial dynamo was being perfected by 
Gramme, Wilde, Siemens, Crompton, and others, that the machines designed 
specially to be good and economical generators of currents proved themselves 
to be far better and more efficient motors than any of the earlier machines 
which had been devised specially to work as electro-magnetic engines. More- 
over, with the perfection of the dynamo came that cheap source of electric 
currents which was destined to supersede the battery. That a dynamo driven 
by asteam engine furnishing currents on a large scale should be a more economical 
source of current than a battery in which zinc was consumed, does not appear 
to have ever occurred to the engineers who, in 1857, discussed the feasibility 
of electric motive power. Indeed, had any of them thought of it, they would 
have condemned the suggestion as chimerical. There was a notion abroad—and 
it persisted into the eighties—that no electric motor could possibly have an 
efficiency higher than 50 per cent. This notion, based on an erroneous under- 
standing of the theoretical investigations of Jacobi, certainly delayed the progress 
of events. Yet the clearest heads of the time understood the matter more truly. 
The true law of efficiency was succinctly stated by Lord Kelvin in 1851, and was 
recognised by Joule in a paper written about the same date. In 1877 Mascart 
pointed out how the efficiency of a given magneto-electric machine rises with its 
speed up to a limiting value. In 1879 Lord Kelvin and Sir William Siemens 
gave evidence before a Parliamentary Committee as to the possible high efficiency 
of an electric transmission of power; and in August of the same year, at the 
British Association meeting at Sheffield, the essential theory of the efficiency of 
electric motors was well and admirably put in a lecture by Professor Ayrton. 
In 1882 the present author designed, in illustration of the theory, a graphic con- 
struction, which has been ever since in general use to make the principle plain. 
The counter-electromotive force generated by the motor when running, which 
Hunt and Tyndall deplored as a defect, is the very thing which enables the 
motor to appropriate and convert the energy of the battery. Its amount 
relatively to the battery’s own electromotive force is the measure of the 
degree to which the energy which would otherwise be wasted as heat is 
utilised as power. Pure science stepped in, then, to confirm the possibility 
of a high efficiency in the electric motor per se. But pure science was 
also brought into service in another way. An old and erroneous notion, which 
even now is not quite dead, was abroad to the effect that the best way of 
arranging a battery was so to group its component cells that its internal resistance 
