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