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gases, whether in a state of translation or of undulation.
The science of mechanics is a portion of natural philosophy,
though at present so large as to need the exclusive atten-
tion of him who would cultivate ‘it profoundly. Astronomy
is the application of physics to the motions of the heavenly
bodies, the vastness of the field causing it, however, to be
regarded as a department in itself. In chemistry physical
agents play important parts. By heat and light we cause
bodies to combine, and by heat and light we decompose
them. Electricity tears asunder the locked atoms of com-
pounds, through their power of separating carbonic acid into
its constituents; the solar beams build up the whole Vege-
table world, and by it the animal, while the touch of the
self-same beams causes hydrogen and chlorine to unite with
sudden explosion and form by their combination a powerful
acid. Thus physics and chemistry intermingle, physical
agents being employed by the chemist as a means to an
end; while in physics proper the laws and phenomena of
the agents themselves, both qualitative and quantitative,
are the primary objects of attention.

My duty here to-night is to spend an hour in telling how
this subject is to be studied, and how a knowledge of it is
to. be imparted to others. When first invited to do this, I
hesitated before accepting the responsibility. It would be
easy to entertain you with an account of what natural phi-
losophy has accomplished. I might point to those applica-
tions of science regarding which we hear so much in the
newspapers, and which we often find mistaken for science
itself. I might, of course, ring changes on the steam-
engine and the telegraph, the electrotype and the photo-
graph, the medical applications of physics, and the million
other inlets by which scientific thought filters into prac-
tical life. That would be easy compared with the task
of informing you how you are to make the study of physics
the instrument of your own culture, how you are to pos-

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