c Senses; the physical
forces, and even inert matter, are also sensitive to its influences,
as I will now demonstrate to you.

In wireless telegraphy it is absolutely necessary that the transmitter
of the electro-magnetic waves should be brought into perfect harmony
with the receiver--without that condition it is impossible to
communicate at a distance; again, a heavy pendulum or swing can, by a
certain force, be pushed, say an inch, from its position of rest, and
each successive push will augment the swing, but only on one
condition, namely, that the force is applied in sympathy with the
pendulum's mode of swing; if the length of the pendulum is 52 feet,
the force must be applied only at the end of each eight seconds, as,
although the pendulum at first is only moving one inch, it will take
four seconds to traverse that one inch, the same as it would take to
traverse 10 feet or more, and will not be back at the original
position till the end of eight seconds; if the force is applied before
that time the swing of the pendulum would be hindered instead of
augmented. Even a steam engine must work under this influence if it is
to be effective; there may be enough force in a boiler to do the work
of a thousand horse-power, but, unless the slide valve is arranged so
that the steam enters the cylinder at exactly the right moment,
namely, in sympathy with the thrust of the piston, no work is
possible.

To understand the next example I want you first to recognise that,
apart from its physical qualities, every material body has certain,
what may be called, traits of character, which belong to it alone;
there is generally one special trait or "partial," namely, the
characteristic which it is easiest for the particular body to
manifest, but I shall show you that by sympathetic action others can
be developed. I have several pieces of ordinary wood, used for
lighting fires, each of which, according to its size and density, has
its special characteristic; if you examined each by itself you would
hardly see that they are different from one another except slightly in
length, but if I throw them down on the table, you would hear that
each of them gives out a clear characteristic note of the musical
scale: to carry this a step forward, I have a long, heavy, iron bar,
about 4 feet long and 2 inches thick, so rigid that no ordinary manual
force can move it out of the straight, and, from mere handling, you
would find it difficult to imagi