Dr. Grey’s method is highly useful in general, so it is particularly excellent in respect of all memorables that are represented by numeral figures. For, when the numeral figures are denoted by letters, collections of them, such as dates, and quantities of all kinds, make short and definite impressions upon the ear; which are not only easy to be remembered, but also preserve the order of the figures without danger of error: whereas neither the impressions which collections of figures make upon the eye, nor those which their enunciations in words at length make upon the ear, can be remembered with facility or precision; because neither figures, nor their names, cohere together, so as that the precedent shall suggest the subsequent; as the letters do in collections of them, capable of being pronounced. When the technical word coincides with, or approaches to, a familiar one, it is remembered with greater facility. Association is every where conspicuous in these things.
It does not appear at all improbable, that the vibrations, which are excited by sounds in the cartilages of the auricle and meatus auditorius, should pass into the small muscles of the auricle, and there occasion automatic motions. And I guess in particular, that in very loud sounds, the cartilages would be made to lie closer to the head. But the smallness of these muscles, and the practice of binding down the ears of new-born children close to the head, which restrains the natural action of these muscles, whatever it might be, prevent our making any certain judgment.
As to the four muscles which belong to the small bones, it appears to me, that since the externus and obliquus lie out of the tympanum, exposed to the common air, and are also so situated, that the externus may receive vibrations from the cartilage of the meatus auditorius, the obliquus from the cartilage of the processus ravianus, into which it is inserted, they must be much more affected by loud sounds, than the internus or musculus stapedis. It follows therefore, that the membrana tympani will be relaxed automatically by loud sounds. Here therefore is another remarkable coincidence between efficient and final causes.
For what reasons the musculus internus, and musculus stapedis, may act peculiarly in weak sounds, is difficult to say. They may perhaps, as was above conjectured of the radiated fibres of the iris, depend chiefly on the influences which descend from the brain, and therefore act always, when the other two will give them leave. It is most probable, that the four muscles act in various proportions and combinations, so as to answer a variety of purposes. But there is very little, that is satisfactory, to be met with in books of anatomy and physiology hitherto, concerning the peculiar minute uses and functions of the several parts of the organ of hearing.
