discharged in abscesses of the brain, one would incline to think, that the external parts of the medulla are instrumental, in respect of the internal. And, on the other hand, one may question, whether in animals of the serpentine form, and those whose brains are comparatively small, and in all those of the polypous kind, the sensorium be not equally diffused over the whole medullary substance, or even over all the living parts. I only hint these things, not presuming even to conjecture, but only to excite those who have proper opportunities, to inquire carefully into these matters.
Cor. IV. If we allow the existence of the æther, and its use in performing sensation, thought, and motion, as it may be inferred from the two foregoing propositions, compared with such other things as follow in these observations, in favour of the doctrine of vibrations; we may conclude that the æther must have a considerable share in the production of many other natural phænomena; and therefore shall have a sufficient foundation for trying how far it will carry us agreeably to the facts. I would recommend this, in a particular manner, to those persons who are much conversant with electrical phænomena; especially as Sir Isaac Newton himself, whose great caution and reservedness, in difficult and doubtful matters, are sufficiently known, has made no scruple to affirm, that the powers of electrical bodies are owing to the action of the æther. See the last paragraph of the Principia.
Scholium. It may be proper to remark here, that I do not, by thus ascribing the performance of sensation to vibrations excited in the medullary substance, in the least presume to assert, or intimate, that matter can be endued with the power of sensation. It is common to all systems, to suppose some motions attendant upon sensation, since corporeal objects must, by their actions, impress some motion upon our bodies, and particularly upon that part which is most nearly related to the sentient principle; i.e. upon the medullary substance, according to the first and second propositions. I lay down these propositions, therefore, as established by the common consent of physicians and philosophers; and upon that foundation proceed to inquire into, and determine, some matters of a more difficult nature; such as, the complex problems concerning sensations, ideas, and motions, and their mutual influences and relations.
The following instance may illustrate this:—The quantity of matter in bodies is always found to be proportional to their gravity: we may therefore either make the quantity of matter the exponent of the gravity, or the gravity the exponent of it, according as either can be best ascertained; notwithstanding that we are entirely at a loss to determine in what mechanical way each atom contributes to the gravity of the whole mass; and even though we should, with some, suppose this effect to be immechanical, and to arise from the immediate agency of God.
