to be removed. It is evident from the nature of vibratory motions, that the medullary substance will not, immediately upon the removal of this object, return to its natural state N, but will remain, for a short space of time, in the preternatural state A, and pass gradually from A to N. Suppose the same object to be impressed again and again, for a sufficient number of times, and it seems to follow, that the medullary substance will be longer in passing from A to N, after the second impression than after the first, after the third impression than second, &c. till, at last, it will not return to its natural original state of vibration N at all, but remain in the preternatural state A, after the vibrations have fallen to a diminutive pitch, their kind and place, or chief seat, and their line of directions, continuing the same. This state may therefore be fitly denoted by a, and, being now in the place of the natural state N, it will be kept up by the heat of the medullary substance, and the pulsation of its arteries. All this seems to follow from the above-mentioned disposition of animal bodies to accommodate themselves to, and continue in, almost any state that is often impressed; which is evident from innumerable both common and medical observations, whatever be determined concerning the manner of explaining and accounting for these facts. For the alterations which habit, custom, frequent impression, &c. make in the small constituent particles, can scarce be any thing besides alterations of the distances, and mutual actions, of these particles; and these last alterations must alter the natural tendency to vibrate. We must, however, here resume the supposition made in the last paragraph, viz. that the several regions of the brain have such a texture as disposes them to those specific vibrations, which are to be impressed by the proper objects in the events of life. And this will much facilitate and accelerate the transition of the state N into a; since we are to suppose a predisposition to the state A, or a.
It will somewhat illustrate and confirm this reasoning, to remark, that musical strings always accommodate themselves to, and lean towards the state into which they were last put. Thus the tone of a musical string either rises or falls upon altering its tension, according as the preceding tension was greater or less than its present tension. Now the small component parts of a musical string must recede from, and approach to, each other, i.e. must oscillate lengthways, during every transverse oscillation of the string. And this must arise from the mutual influences of the component particles tending to their last superinduced state. Let us suppose something analogous to this to take place in the component molecules of the brain, the molecules of the molecules, &c. and it will follow, that A may overpower N, and a become the natural state. Now, since the human body is composed of the same matter as the external world, it is reasonable to expect, that its component particles should be
