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and distinction, all those synthetic charms, and that logical beauty of form, which captivated so many heads and hearts, when this doctrine first made its appearance on the stage of science under the patronage and auspices of Dr. Hartley.
The Hartleian system may be considered principally as a mental system, at least that part of it which consists of the doctrine of vibrations; and ought, therefore, to be more properly referred to metaphysics than to morals. His theory of vibrations is, however, so connected and mixed
with his moral speculations and principles, that it becomes absolutely necessary, for the right understanding of them, that the reader should have some general con. ception or idea of the nature of bis mental philosophy. In giving an outline of this part of the Doctor's work, we will endeavour to be as brief as perspicuity and the abstract and recondite nature of the doctrine will admit.
By Dr. Hartley's own account, as well as from that of his zealous and respectable followers, Drs. Priestley and Belsham, it would appear, that the first suggestions which he received of the doctrine of vibrations were from some casual hints contained in the works of Sir Isaac Newton. In that philosopher's “ Principia,” and in the “ Queries” at the
end of his Optics, we find the remarks alluded to. Sir Isaac Newton supposes, that a very subtile and elastic fluid, which he calls Æther, for the sake merely of giving it a name, is diffused through the pores of all gross bodies, as well as through the open spaces that are void of gross matter.
matter. He poses, likewise, that it is rarer in the pores of bodies than in open spaces, and even rarer in small pores and dense bodies than in large pores and rare bodies; and also that its density increases in receding from gross matter; so, for instance, as to be greater at the one-hundredth of an inch from the surface of any body than at its surface; and so on in a corresponding proportion. To the action of this æther he ascribes the attractions of gravitation and cohesion, the attractions and repulsions of electrical bodies, the mutual influences of bodies and light upon each other, the effects and communications of heat, and the performance of animal sensation and motion. In the “Queries” attached to Sir Isaac's Optics we find the following :-“ Do not the
rays of light, in falling upon the bottom of the eye, excite vibrations in the tunica retina ? Which vibrations being propagated along the solid fibres of the optic nerves into the brain, cause the sense of seeing. For, because dense bodies conserve
their heat a long time, and the densest bodies conserve their heat the longest, the vibrations of their parts are of a lasting nature; and, therefore, may be propagated along solid fibres of uniform dense matter, to a great distance, for conveying into the brain the impressions made upon all the organs of
For that motion which can continue long in one and the same part of a body can be propagated a long way from one part to another, supposing the body homogeneal; so that the motion may not be reflected, refracted, interrupted, or disordered, by any unevenness of the body.” “Quest. 13.-Do not several sorts of
make vibrations of several bignesses, which, according to their bignesses, excite sensations of several colours, much after the manner that the vibrations of the air, according to their several bignesses, excite sensations of several sounds ? And, particularly, do not the most refrangible rays excite the shortest vibrations for making a sensation of deep violet, the least refrangible the largest for making a sensation of deep red, and the several intermediate sorts of rays, vibrations of several intermediate bignesses, to make sensations of the several intermediate colours ?”
From the suggestions contained in these quotations, the Doctor founded his whole system of vibrations. His doctrine may be briefly comprehended in the following summary :-All our ideas and sensations are derived from external objects acting through the medium of our organs of sense or perception; namely, sight, taste, hearing, feeling, and smelling. These different organs consist of nerves suited to their nature; and by these nerves being affected by the external impulse of various bodies, they convey these outward impressions to the brain, which is the great reservoir or common centre of the nervous influence. The nerves and the brain are considered to be the same in their natures and
properties. Whether these nerves resemble tubes, for the purpose of conveying a fluid, or they partake of the nature of cords or strings, is not fully decided ; but Drs. Hartley and Priestley are inclined to the latter supposition, that the nerves vibrate someway analogous to a stringed instrument of music.
That sensations are conveyed to the brain in the form of vibration, is rendered highly probable from the manner in which the senses of seeing and hear. ing are affected. It is maintained that the retina is affected by the rays of light falling upon it with a tremulous motion, and that this impression or motion continues for some time, and gradually seems
to die away, when the object which produced it is removed. If a person keep his eye fixed for any length of time upon a luminous object, and afterwards shut it, he will observe that the impression he feels seems to partake of the nature of a tremu. lous or vibratory motion. If the nerves employed in vision are affected at their extremity in this tremulous manner, does it not become exceedingly probable, that the impression is conveyed to the brain by a continuation of this same motion, seeing that the brain is precisely of the same nature as the nerves, and consequently that an idea is nothing
, more than a vibratory motion of the parts of the brain ?
As the texture of the nerves, as far as observations can be made, appears to be the same in all the senses or organs of perception, it is but reasonable to infer from the analogy of structure, that if impressions on one sense be conveyed to the brain by vibrations, that the impressions upon the other senses will be conveyed in the same manner. In the organ of hearing this is very probable. The professors in the science of “ Acoustics” tell us, that sound is produced by the agitation or vibratory motion of the air ; and since this vibratory action must consist of successive pulses, it will communi