velocity in the greatest heights of the heavens, gradually decreases, and at length terminates,' and comes to nothing, in what is immoveable, viz. the earth.

On the other hand, let the nature enquired into be that other motion of rotation, famousą among astronomers, and opposite and contrary to the diurnal motion, viz, the motion from west to east, which the astronomers attribute to the planets and sphere of the fixed stars, but Coper-} . nicus and his followers assign likewise to the earth; and let it be sought whether there is any such motion in nature, or whether it be only imaginary, and supposed for the readiness and convenience of calculation, and the sake of the beauty and regularity of a system, so as to make the celestial motions performed in perfect cir*, ! cles.

This motion is by no means proved true and real in the higher celestial bodies, neither from hence, that a planet does not, in its diurnal motion, return to the same fixed star again, nor from hence, that the poles of the zodiac differ from the poles of the world, which are the two things whereon this motion is founded. For, the first phænomenon is well solved, by the sup- · position of antecedence and dereliction, and the second by spiral lines, so that the inequality of the revolution, and the declination to the tro

pics, may be rather modifications of the same diurnal motion, than contrary motions, or performed about different poles. And if we may here, for once, side with the vulgar, and leave the fictions of astronomers and the schools, (who in many cases, without reason, offer violence to the senses, and rather affect obscurities,) we judge this motion to be to the sense, such as we have above described it, from a model we once had purposely made of iron wire to represent it.

But it may be a crucial instance in this enquiry, if it shall be found from any history worthy of credit, that there was a comet, which did not revolve in a manifest consent (though ever so irregularly) with the visible diurnal motion; but rather to the opposite part of the heavens, for then it will be free to judge that some such motion, contrary to the visible diurnal rotation, may exist in nature. But if nothing of this kind can be found, such a motion should not be embraced, but recourse be had to other crucial instances about it *.

Again; suppose the nature sought was gravity, this will be the cross-road. Heavy and ponderous bodies must either have a natural tendency to the centre of the earth, on account

* See the author's Specimen of animated Astronomy.

of their proper mechanism, or else be attracted by the corporeal mass thereof, as by a collec tion of bodies of the same nature, and so be carried to it by consent.

If the latter be the cause, it will follow, that the nearer all heavy bodies approach to the earth, the stronger, and with the greater force and velocity they will tend to it; but the farther they are from it, the weaker and the slower, and this to a certain distance; whence, if they were removed so far from the earth, as that the virtue thereof could not act upon them, they would remain pendulous, like the earth itself, without falling*.

And with regard hereto this may be a crucial instance. Take a clock that moves by weights, and another that moves by a steel spring; let them be exactly adjusted, that neither of them may go faster than the other; place the clock that goes with weights upon the top of some very high building; keep the other below; then carefully observe if the clock above move slower than usual, on account of the diminished virtue of its weight. Let the same experiment be made in the deepest mines, to shew whether such a clock will not move faster there, for the

* Compare this with Sir Isaac Newton's Laws of Motion. See his Princip. in init.

contrary reason; and if the virtue of the weights shall be found diminished above, and increased below the surface of the earth, let the attraction of the terrestrial mass be received as the cause of weight or gravity.*.

Again; let the nature sought be the verticity of the magnetic needle; and the cross-way will be this: the touch of the magnet must either of itself necessarily give iron the property of pointing north and south; or else only excite and prepare, or fit the iron for the purpose; and the motion itself (as Gilbert conceives, and laboriously endeavours to prove) be given by the presence of the earth; and, therefore, the particulars, which he has with much sagacity and industry discovered, amount to this; that an iron nail, which has long continued in the direction of north and south, may by that mere continuance receive a verticity, without the touch of the magnet; as if the earth itself, though it operates weakly, by reason of its distance, (for the surface or external crust of the earth has no magnetic virtue, according to him,) should yet, in so great a length of time, supply the defect of the loadstone, excite the iron, and afterwards make it comply when thus excited. And again; that if ignited iron be quenched, point

See Sir Isaac Newton's Principia, passim.

ing in the direction of north and south, it also receives a verticity without the magnetic touch, as if the parts of the iron, put in motion by the ignition, and afterwards contracting themselves in the very instance, of quenching, were more susceptive and sensible of the virtue rising from the earth, than at another time; and thence become animated: but these particulars, though well observed, do not clearly prove his point.

This may be a crucial instance in the present case. Mark the poles of a terella, and place them east and west; then lay an untouched needle thereon, and let it remain for six or seven days. The needle, no doubt, whilst it lies upon the magnet, will quit the poles of the world, and conform to those of the magnet; and therefore, as long as it remains thus, it points east and west. But if the needle shall be found, when removed from the terella, or magnet, and placed upon its pin, immediately to turn north and south, or by degrees to move into that direction, then the earth's presence is to be admitted for the cause; but if it turns as before, east and west, or loses its verticity, then that cause should be accounted doubtful, and farther enquiry be made

See the Sylva Sylvarum, under the article Magnetism.