The chemical composition of a body might be noted by its electric resistance and the latter verified by the telephone; that is to say, by the ear.

Or, to take a more subtle example.

We might make calculations with sounds of which we have studied the harmonic relations as we do nowadays with figures.

A sum in rule of three might even be solved sonorously; for, given three sounds, the ear can find a fourth which should have the same relation to the third as the second to the first.

Every musical ear performs this operation easily; now, this fourth sound, what else is it but the fourth term in a rule of three?
And by taking into consideration the number of its vibrations a numerical solution would be found to the problem.