A very slight degree of reflection is sufficient to evince, that we could not have had the idea of resistance, which forms so great a part of what we call our idea of matter, without the feelings which attend muscular action. Resistance means a force opposed to a force; the force of the object, opposed to the force which we apply to it. The force which we apply is the action of our muscles, which is only known to us by the feelings which accompany it. Our idea of resistance, then, is the idea of our own feelings in applying muscular force. It is true, that the mere feeling of the muscles in action is not the only feeling concerned in the case. The muscles move in consequence of the Will; and what the Will is, we are not as yet prepared to explain. What is necessary at present is, not to shew all the simple feelings which enter into the feeling of resistance; but to shew {44} that the simple feeling of muscular action is one of them. The feeling of resistance admits of great varieties. The feeling of a plate of iron is one thing, the feeling of a blown bladder is another, the feeling of quicksilver is a third, the feeling of water a fourth, and so on. The feeling of weight, or attraction, is also a feeling of resistance. {45} SECTION VIII. SENSATIONS IN THE ALIMENTARY CANAL. When the sensations in the alimentary canal become acutely painful, they are precise objects of attention to every body. There is reason to believe that a perpetual train of sensations is going on in every part of it. The food stimulates the stomach. It undergoes important changes, and, mixed with some very stimulating ingredients, passes into the lower intestines; in every part of which it is still farther changed. The degree, and even the nature, of some of the changes, are different, according as the passage through the canal is slower, or quicker; they are different, according to the state of the organs, and according to the nature of the food. Of the multitude of sensations, which must attend this process, very few become objects of attention; and, in time, an incapacity is generated, of making them objects of attention. They are not, however, as we shall afterwards perceive, feeble agents, or insignificant elements, in the trains of thought. They are of that class of feelings, to which we have already been under the necessity of alluding; a class, which serve as antecedents, to feelings more interesting than themselves; and from which the attention is so instantaneously drawn, to the more interesting feelings by which they are succeeded, that we are as little sensible of their existence, as we often are of the {46} sound of the clock, which may strike in the room beside us, and of course affect our ear in the usual manner, and yet leave no trace of the sensations behind.