Prof. J. Perry lately delivered a lecture on this subject at the Society
of Arts, London, which contains in an epitomized form the salient points
of the hopes and fears of the more sanguine spirits of the electrical
world. Prof. Perry is one of the two professors who have been dubbed the
"Japanese Twins," and whose insatiate love of work induced one of our
most celebrated men of science to say that they caused the center of
experimental research to tend toward Tokyo instead of London. Professors
Ayrton and Perry have for some time been again resident in England, but
it is evident that they did not leave any of their energy in Japan, for
those who know them intimately, know that they are pursuing numerous
original investigations, and that so soon as one is finished, another
is commenced. It would have been difficult then to have found an abler
exponent of the future of electricity.
Prof. Perry, after referring to what might have been said of the great
things physical science has done for humanity, plunged into his subject.
The work to be done was vast, and the workers altogether out of
proportion to the task.
The methods of measurement of electricity are not generally understood.
Perhaps when electricity is supplied to every house in the city at a
certain price per horse power, and is used by private individuals for
many different purposes, this ignorance will disappear. Electrical
energy is obtained in various ways, but the generators get heated; and
one great object of inventors is to obtain from machines as much as
possible electrical energy of the energy in the first place supplied to
such machine. The lecturer called particular attention to the difference
between electricity and electrical energy, and attempted to drive home
the fundamental conceptions of electrical science by the analogies
derivable from hydraulics. A miller speaks not only of quantity of
water, but also of head of water. The statement then of quantity of
electricity is insufficient, except we know the electrical property
analogous to head of water, and which is termed electrical potential. A
small quantity of electricity of high potential is similar to a small
quantity of water at high level. The analogies between water and
electricity were collected in the form of a table shown on a wall sheet
as follows:
We Want to Use Water. We Want to Use Electricity.
1. Steam pump burns coal, 1. Generator burns zinc, or
and lifts water to a higher uses mechanical power, and
level. lifts electricity to a higher
level or potential.
2. Energy available is 2. Energy available is
amount of water lifted x amount of electricity x difference
difference of level. of potential.
3. If we let all the water 3. If we let all the electricity
flow away through channel flow through a wire from one
to lower level without doing screw of our generator to the
work, its energy is all other without doing work, all
converted into heat because the electrical energy is
of frictional resistance of converted into heat because of
pipe or channel. resistance of wire.
4. If we let water work a 4. If we let our electricity
hoist as well as flow through work a machine as well as
channels, less water flows flow through wires, less flows
than before, less power is than before, less power is
wasted in friction. wasted through the resistance
of the wire.
5. However long and narrow 5. However long and thin
may be the channels, the wires may be, electricity
water maybe brought from may be brought from any distance
distance, however great, however great, to give
to give out almost all its out almost all its original
original energy to a hoist. energy to a machine. This requires
This requires a great head a great difference of
and small quantity of water. potentials and a small current.
The difference between potential and electro-motive force was explained
thus: "difference of potential" is analogous with "difference of
pressure" or "head" of water, howsoever produced; whereas electromotive
force is analogous with the difference of pressure before and behind a
slowly moving piston of the pump employed by an unfortunate miller to
produce his water supply. Electricians have very definite ideas upon
the subject they are working at, and especial attention is paid to the
measurements on which their work depends. Examples of these measurements
were shown by the following tables on wall sheets: