Since grave sounds are in general loud, acute ones weak, the relaxation of the membrana tympani, which first attends upon loud sounds automatically, will afterwards, by association, be made to attend upon grave ones, even though they are not loud; and, in like manner, the membrane will be tense, from acute sounds, though they should be strong; i.e. the membrane will, by association, be fitted to vibrate isochronously with the several tones; just as the convexity of the cornea is made by association to suit itself to the several distances. The accommodation is at first gross in both cases; but is perfected afterwards from the view of pleasure and convenience, by means of the frequent recurrency of the actions. See Prop. XXII. Cor. I.
We seem also to have a voluntary power of preparing the ear previously for very strong, or very weak sounds, which we expect to hear, just as it was before observed of the eye, that we can suit it previously to see at an expected distance. The generation of these powers is the same as that of the other voluntary ones.
Section VI
THE DESIRES OF THE SEXES TOWARDS EACH OTHER.
Here we are to observe, first, that when a general pleasurable state is introduced into the body, either by direct impressions, or by associated influences, the organs of generation must sympathize with this general state, for the same reasons as the other parts do. They must therefore be affected with vibrations in their nerves, which rise above indifference into the limits of pleasure from youth, health, grateful aliment, the pleasures of imagination, ambition, and sympathy, or any other cause, which diffuses grateful vibrations over the whole system.
Secondly, As these organs are endued with a greater degree of sensibility than the other parts, from their make, and the peculiar structure and disposition of their nerves, whatever these be, we may expect, that they should be more affected by these general pleasurable states of the nervous system than the other parts.
