Casting a retrospective glance at the four methods of transmission of power
which have been examined, it would appear that transmission by ropes forms
a class by itself, while the three other methods combine into a natural
group, because they possess a character in common of the greatest
importance. It may be said that all three involve a temporary
transformation of the mechanical power to be utilized into potential
energy. Also in each of these methods the efficiency of transmission is
the product of three factors or partial efficiencies, which correspond
exactly--namely, first, the efficiency of the instrument which converts
the actual energy of the prime mover into potential energy; second, the
efficiency of the instrument which reconverts this potential energy into
actual energy, that is, into motion, and delivers it up in this shape
for the actual operations which accomplish industrial work; third, the
efficiency of the intermediate agency which serves for the conveyance of
potential energy from the first instrument to the second.
This last factor has just been given for transmission by electricity. It
is the exact correlative of the efficiency of the pipe in the case of
compressed air or of pressure water. It is as useful in the case of
electric transmission, as of any other method, to be able, in studying the
system, to estimate beforehand what results it is able to furnish, and for
this purpose it is necessary to calculate exactly the factors which compose
the efficiency.
In order to obtain this desirable knowledge, the author considers that the
three following points should form the aim of experimentalists: First,
the determination of the efficiency, K, of the principal kinds of
magneto-electric, or dynamo-electric machines working as generators;
second, the determination of the efficiency, K1, of the same machines
working as motors; third, the determination of the law according to which
the magnetism of the cores of these machines varies with the intensity of
the current. The author is of opinion that experiments made with these
objects in view would be more useful than those conducted for determining
the general efficiency of transmission, for the latter give results only
available under precisely similar conditions. However, it is clear that
they have their value and must not be neglected.
There are, moreover, many other questions requiring to be elucidated by
experiment, especially as regards the arrangement of the conducting wires:
but it is needless to dwell further upon this subject, which has been ably
treated by many English men of science--for instance, Dr. Siemens and
Professor Ayrton. Nevertheless, for further information the author would
refer to the able articles published at Paris, by M. Mascart, in the
_Journal de Physique_, in 1877 and 1878. The author would gladly have
concluded this paper with a comparison of the efficiencies of the four
systems which have been examined, or what amounts to the same thing--with a
comparison of the losses of power which they occasion. Unfortunately, such
a comparison has never been made experimentally, because hitherto the
opportunity of doing it in a demonstrative manner has been wanting, for the
transmission of power to a distance belongs rather to the future than to
the present time. Transmission by electricity is still in its infancy; it
has only been applied on a small scale and experimentally.
Of the three other systems, transmission by means of ropes is the only one
that has been employed for general industrial purposes, while compressed
air and water under pressure have been applied only to special purposes,
and their use has been due much more to their special suitableness for
these purposes than from any considerations relative to loss of power.
Thus the effective work of the compressed air used in driving the
tunnels through the Alps, assuming its determination to be possible, was
undoubtedly very low; nevertheless, in the present state of our appliances
it is the only process by which such operations can be accomplished. The
author believes that transmission by ropes furnishes the highest proportion
of useful work, but that as regards a wide distribution of the transmitted
power the other two methods, by air and water, might merit a preference.
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