placed as to be conveniently electrified without electrifying the plate at the same time; the little sphere of glass will describe an orbit about the ring, and will turn at the same time about its own axis, the poles of its rotation being nearly at right angles to the plane of its orbit. Here again, if the emission of light from the electrical globe were as constant as the supplies from the şun to the planets, the motion of this sphere would resemble the motion of the earth, as nearly in its perpetuity, as it doth in some other respects.

In all these instances, a resisting medium does not hinder motion, but actually promotes it, and is one of the immediate causes of it; and, were these little experiments as adequate to the greater phænomena of the universe as they are analogous to them, would render the motion perpetual. An hypothetical train of reasoning might lead us to conclude, that if less matter were in the space, the motion would be more free, and continue much longer: upon the supposed strength of which conclusion, (if a little geometry were interwoven with it,) we might think it necessary to get rid of the air and of all sensible matter; and then we should

VOL, VIII.

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should also get rid of the causes of motion. In a word, the facts now before us shew how much we should lose by the application of this unphilosophical method; which would promote the success of these experiments, just as much as we should enable a man to run faster, were we to rid him of the incumbrance of his boots and spurs by cutting off his legs.

I think it hardly necessary to observe, as the thing is so obvious, that although the mode of operation in each of these experiments is very different, yet the effects in all of them are deducible from the same causes, fire and air, ordained in a wonderful manner to co-operate with each other.

ON CHAP. VI.

Page 76, 1. 14. &c. It hath been hinted to me by a learned friend who saw this chapter in manuscript, that the geometrical argument of Dr. Keil, though it makes but an indifferent figure in the manner he hath stated it, may nevertheless be applied to demonstrate an interstitial vacuum between the

parts of bodies. And thus much indeed it may warrant us to affirm, that if the world is filled with an homogeneous matter, all the

particles

particles of which are exact spheres, of equal sizes, and all of them in contact; an inter · stitial vacuum must be the consequence: and the ratio of the full space to the empty space, will be as the solid content of a sphere to the difference between that and the content of a cube of the same diameter.

But

then, how many suppositions is it necessary to make, before the way is clear to such a conclusion? and when we have attained it, it leaves my argument but where it found it. For unless these homogeneous spheres are out of contact, (the contrary to which is supposed in the demonstration,) a motion propagated amongst them will be mechanical; and that is all I am contending for. But such mathematical reasonings are all of them wide of the purpose, only tempting us to ramble from the real merits of the cause, and to multiply words, without knowledge; an observation which ought to be as freely applied to what I have hitherto said in answer to the demonstration, as to the demonstration itself. If we leave geometry to take its chance, and make a transition to reason and observation, it will be hard enough to shew, that within the whole created system of the world there is any space capable of holding a particle

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a particle of matter, which has not such a particle in it. A subtile substance, (that of fire or light,) not to be excluded by the surfaces of the most solid body, is in perpetual agitation, and ready, as experience teaches, to find its way into every channel capable of receiving it. It has likewise been proved above, that between the particles of this substance there is no repulsive power to keep them at a distance from each other: and as Sir Isaac Newton hath given us some fine experiments in his Treatise of Optics, whence it is highly probable that even the particles of light are of various sizes, they will on that account fill up any given space the more completely; and the interstitial vacuities, if they can be called such, will vanish into something not worth regarding, because it is impossible to be conceived, unless the imagination should put a trick upon itself; which, I believe, is sometimes the case, when it is contemplating such objects as are beyond its reach. If we keep within the limits of our understanding, and attend to nature itself as it is displayed before our eyes, we may express both safely and truly all that is necessary to be affirmed upon this occasion, in the following words, taken from

the

the discourse of Timæus Locrus the Pythagorean-Πυρ μεν ων δια των λεπ]ομερειαν δια πάντων ηκεν, αήρ τε δια των άλλων έξω πυρος ύδωρ δε δια τας γας. Απαντα δ' ων πληρη εντι, εδεν κενεον απολιπόντα— Fire, by reason of

its subtilty, penetrates into all things; air, "into all the other elements, except fire;

and water into earth: so that the world "is full of matter, and there is no vacuum "left in it." N. B. This discourse is subjoined to Plato's Timæus; or it may be found in Gale's Opuscula Mythologica.

ON BOOK III. CHAP. II.

An Addition to the Note at Page 207.

A

SI have here dropped an hint concern

ing the danger which is to be apprehended from electricity; it may not be amiss to give some short account of its good effects, so far as they have fallen under my own ob

servation.

A girl of about 12 years of age, the daughter of a shepherd in this parish of Wadenho in North

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