_ON THE NATURE AND OBJECTS OF MACHINERY._
Machines do not create or consume, but only transmit and apply
power; and it is only by conceiving of power as a constant element,
independent of every kind of machinery, that the learner can reach
a true understanding of the nature of machines. When once there is
in the mind a fixed conception of power, dissociated from every
kind of mechanism, there is laid, so to speak, a solid foundation
on which an understanding of machines may be built up.
To believe a fact is not to learn it, in the sense that these terms
may be applied to mechanical knowledge; to believe a proposition
is not to have a conviction of its truth; and what is meant by
learning mechanical principles is, as remarked in a previous place,
to have them so fixed in the mind that they will involuntarily
arise to qualify everything met with that involves mechanical
movement. For this reason it has been urged that learners should
begin by first acquiring a clear and fixed conception of power, and
next of the nature and classification of machines, for without the
first he cannot reach the second.
Machines may be defined in general terms as agents for converting,
transmitting, and applying power, or motion and force, which
constitute power. By machinery the natural forces are utilised,
and directed to the performance of operations where human strength
is insufficient, when natural force is cheaper, and when the rate
of movement exceeds what the hands can perform. The term "agent"
applied to machines conveys a true idea of their nature and
functions.
Machinery can be divided into four classes, each constituting a
division that is very clearly defined by functions performed, as
follows:--
_First._ Motive machinery for utilising or converting the natural
forces.
_Second._ Machinery for transmitting and distributing power.
_Third._ Machinery for applying power.
_Fourth._ Machinery of transportation.
Or, more briefly stated--
Motive machinery.
Machinery of transmission.
Machinery of application.
Machinery of transportation.
These divisions of machinery will next be treated of separately,
with a view of making the classification more clear, and to explain
the principles of operation in each division. This dissertation
will form a kind of base upon which the practical part of the
treatise will in a measure rest. It is trusted that the reader will
carefully consider each proposition that is laid down, and on his
own behalf pursue the subjects farther than the limits here permit.
(1.) To what three general objects are machines directed?--(2.)
How are machines distinguished from other works or
structures?--(3.) Into what four classes can machinery be
divided?--(4.) Name one principal type in each of these four
divisions.