tenth respectively. It is also an evidence and illustration of the second; shewing, not only that the state of the medullary substance is changed, according to the several natures of the ideas which are presented to the mind; but also shewing, in general, of what kind this change is, and in what manner it is effected.
For these complex vibrations may consist of so many parts co-existent and successive, and these parts may so alter and exalt one another, as that the resulting agitations in the medullary substance may no longer be miniature vibrations, but vivid ones equal to those excited by objects impressed on the senses. This process may be farther favoured by a mixture of vivid real impressions among the ideas, by the irritability of the medullary substance, by a previous disposition to the vibrations to be excited, &c.
Cor. I. When the complex miniature vibrations are thus exalted in degree, we are to conceive, that the corresponding complex ideas are proportionally exalted, and so pass into intellectual affections and passions. We are therefore to deduce the origin of the intellectual pleasures and pains, which are the objects of these affections and passions, from the source here laid open.
Cor. II. Since the present proposition unfolds the nature of affections and will, in the same manner, and from the same principles, as the twelfth does that of ideas, intellect, memory, and fancy; it follows, that all these are of the same original and consideration, and differ only in degree, or some accidental circumstances. They are all deducible from the external impressions made upon the senses, the vestiges or ideas of these, and their mutual connexions by means of association, taken together and operating on one another.
Cor. III. It follows also from this proposition, that the intellectual pleasures and pains may be greater, equal, or less, than the sensible ones, according as each person unites more or fewer, more vivid or more languid, miniature vibrations in the formation of his intellectual pleasures and pains, &c.
Cor. IV. It is evident, that all the vibrations which belong to ideas, and intellectual affections, must reside in the brain, or even in the most internal parts of it, not in the spinal marrow or nerves. The brain is therefore the seat of the rational soul, i.e. of the soul, as far as it is influenced by reasons and moral motives, even though we should admit, that the spinal marrow and nerves, are, in part, the sensorium, or the seat of the sensitive soul; which is some argument, that this ought not to be
