It is most certain that the cause of pleasure in all our senses originates from the justness of proportion, and that disproportion never creates a pleasing sensation. The lad whom Mr. Chesselden restored to sights was at first most delighted with those objects which were regular and smooth on the surface; from this it is plain that the ideas we entertain of beauty from the eye originates from regularity and proportion; it is the same with the sense of feeling, smooth, round, and uniform bodies are more pleasing than those which are rough and irregular; why should not therefore the same preference be given by the ear to the proportion of sounds?
Sound has, in common with light, the property of being extensively diffused; and also admits of reflection. The laws of this reflection, it is true, are less understood: all we know is, that sound is reflected by hard bodies, and that their being hollow, sometimes increases the reverberation. A wall or a mountain sometimes reflects sounds so distinct that we are almost induced to suppose it proceeds from them rather than from an opposite quarter. Vaults and hollow rocks also produce distinct echoes.
The internal part of the ear is particularly formed for reflecting sounds, and may, in some measure, be compared to the cavern of a rock. In this cavity sounds are repeated, and by that means conveyed to the membranous part of the lamina, which being an expansion of the auditory nerves transmits them to the mind. The internal cavity of the ear, which is fashioned out in the temporal bone, like a cavern cut into a rock, seems to be fitted for the purposes of echoing sound with the greatest precision.
One of the most common complaints in old age is deafness, which probably proceeds from the rigidity of the nerves in the labyrinth of the ear, augmenting as we advance in years, and when the membranous part of the lamina becomes ossified deafness is the consequence, and is in that case incurable. It sometimes happens from a stoppage of the wax, but it may then be relieved by art. In order to know whether the defect be an internal or art external one, let the deaf person put a repeating watch into his mouth, and if he hears it strike, he may be assured that his disorder proceeds from an external cause, and may be, in some measure, relieved.