h throw into vibration the air forced
between them from the lungs, thus producing musical sounds. These
membranes are, to some extent, under the control of the will, and it
is found that they can be so modified by exercise as to produce notes
of a clearer and more melodious character. This exercise we call the
education of the voice. We may choose for our exercise songs new or
old, festive or solemn; the education of the voice being the object
aimed at, the songs may be regarded as the means by which this
education is accomplished. I think this expresses the state of the
case more clearly than if we were to call the songs a branch of
education. Regarding also the education of the human mind as the
improvement and development of the mental faculties, I shall consider
the study of Physics as a means towards the attainment of this end.
From this point of view, I degrade Physics into an implement of
culture, and this is my deliberate design.

The term Physics, as made use of in the present Lecture, refers to
that portion of natural science which lies midway between astronomy
and chemistry. The former, indeed, is Physics applied to 'masses of
enormous weight,' while the latter is Physics applied to atoms and
molecules. The subjects of Physics proper are therefore those which
lie nearest to human perception: light and heat, colour, sound,
motion, the loadstone, electrical attractions and repulsions, thunder
and lightning, rain, snow, dew, and so forth. Our senses stand
between these phenomena and the reasoning mind. We observe the fact,
but are not satisfied with the mere act of observation: the fact must
be accounted for--fitted into its position in the line of cause and
effect. Taking our facts from Nature we transfer them to the domain
of thought: look at them, compare them, observe their mutual relations
and connexions, and bringing them ever clearer before the mental eye,
finally alight upon the cause which unites them. This is the last act
of the mind, in this centripetal direction--in its progress from the
multiplicity of facts to the central cause on which they depend. But,
having guessed the cause, we are not yet contented. We set out from
the centre and travel in the other direction. If the guess be true,
certain consequences must follow from it, and we appeal to the law and
testimony of experiment whether the thing is so. Thus is the circuit
of thought completed,--from without inward, from multiplici