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and, if we may so speak, provided certain materials; and, afterwards, have committed to another Being, out of these materials, and in fubordination to these rules, the task of drawing forth a creation: a fuppofition which evidently leaves room, and induces indeed a neceffity, for contrivance. Nay, there may be many fuch agents, and many ranks of these. We do not advance this as a doctrine either of philofophy or of religion; but we say that the fubject may fafely be represented under this view, because the Deity, acting himself by general laws, will have the fame confequences. upon our reafoning, as if he had prescribed thefe laws to another. It has been faid, that the problem of creation was, "attraction and matter being given, to make a world out of them" and, as above explained, this statement perhaps does not convey a false idea.

We have made choice of the eye as an inftance upon which to reft the argument of this chapter. Some fingle example was to be propofed; and the eye offered itself under the advantage of admitting of a ftrict comparison with optical inftruments. The ear, it is pro

bable,

But we

bable, is no lefs artificially and mechanically adapted to its office, than the eye. know lefs about it: we do not fo well underftand the action, the use, or the mutual dependency of its internal parts. Its general

form, however, both external and internal, is fufficient to fhew that it is an inftrument adapted to the reception of found; that is to fay, already knowing that found confifts in pulfes of the air, we perceive, in the ftructure of the ear, a fuitablenefs to receive impreffions from this fpecies of action, and to propagate these impreffions to the brain. For of what does this ftructure confift? An external ear (the concha), calculated, like an eartrumpet, to catch and collect the pulfes of which we have spoken; in large quadrupeds, turning to the found, and poffeffing a configuration, as well as motion, evidently fitted for the office: of a tube which leads into the head, lying at the root of this outward ear, the folds and finufes thereof tending and conducting the air towards it: of a thin membrane, like the pelt of a drum, ftretched across this paffage upon a bony rim: of a chain of moveable, and infinitely curious, bones, forming a communication, and the only communi

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cation that can be observed, between the membrane laft mentioned and the interior channels and receffes of the fkull: of cavities, fimilar in fhape and form to wind inftruments of mufic, being spiral or portions of circles; of the eustachian tube, like the hole in a drum, to let the air pass freely into and out of the barrel of the ear, as the covering membrane vibrates, or as the temperature may be altered: the whole labyrinth hewn out of a rock: that is, wrought into the fubftance of the hardest bone of the body. This affemblage of connected parts constitutes together an apparatus, plainly enough relative to the tranfmiffion of found, or of the impulfes received from found, and only to be lamented in not being better understood.

The communication within, formed by the fmall bones of the ear, is, to look upon, more like what we are accustomed to call machinery, than any thing I am acquainted with in animal bodies. It feems evidently defigned to continue towards the fenforium the tremulous motions which are excited in the " membrane of the tympanum," or what is better known by the name of the "drum of the ear." The compages of bones confifts of four, which are fo difpofed, and fo hinge upon one another, as that, if the

membrane,

membrane, the drum of the ear, vibrate, all the four are put in motion together; and, by the refult of their action, work the base of that which is the laft in the feries, upon an aperture which it clofes, and upon which it plays, and which aperture opens into the tortuous canals that lead to the brain. This laft bone of the four is called the flapes. The office of the drum of the ear is to spread out an extended surface, capable of receiving the impreffions of found, and of being put by them into a state of vibration. The office of the stapes is to repeat these vibrations. It is a repeating frigate, ftationed more within the line. From which account of its action may be understood, how the fenfation of found will be excited, by any thing which communicates a vibratory motion to the ftapes, though not, as in all ordinary cafes, through the intervention of the membrana tympani. This is done by folid bodies applied to the bones of the skull, as by a metal bar held at one end between the teeth, and touching at the other end a tremulous body. It likewife appears to be done, in a confiderable degree, by the air itself, even when this membrane, the drum of the ear, is greatly damaged. Either in the natural or præternatural

ternatural ftate of the organ, the use of the chain of bones is to propagate the impulse in a direction towards the brain, and to propagate it with the advantage of a lever; which advantage confifts in increafing the force and ftrength of the vibration, and at the fame time diminishing the space through which it ofcillates: both of which changes may augment or facilitate the fill deeper action of the auditory nerves.

The benefit of the euftachian tube to the organ, may be made out upon known pneumatic principles. Behind the drum of the ear is a fecond cavity or barrel, called the tympanum. The euftachian tube is a flender pipe, but fufficient for the paffage of air, leading from this cavity into the back part of the mouth. Now, it would not have done to have had a vacuum in this cavity; for, in that cafe, the preffure of the atmosphere from without would have burft the membrane which covered it. Nor would it have done to have filled the cavity with lymph or any other fecretion; which would neceffarily have obftructed, both the vibration of the membrane, and the play of the fmall bones. Nor, laftly, would it have done to have occupied the space

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