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Another argument, favouring this hypothesis, is drawn from a proposition of the same Mr. Newton, where he determines the force with which the moon moves the sea in producing the tides, where he says the density of the moon is to that of the earth, as 680 to 387, or as 9 to 5 nearly : therefore the body of the moon is denser than our earth, &c. Now, if the moon be more solid than the earth, as 9 to 5, why may we not reasonably suppose the moon, being a small body and a secondary planet, to be solid earth, water, and stone, and this globe to consist of the same materials, only four. ninths thereof to be cavity, within and between the internal spheresa

To those that shall inquire of what use these included globes can be, it must be allowed, that they can be of very little service to the inhabitants of this outward world ; nor can the sun be serviceable to them, either with his light or heat. But since it is now taken for granted that the earth is one of the planets, and that they all are with reason supposed habitable, though we are not able to define by what sort of animals ; and since we see all the parts of the creation abound with animate beings, as the air with birds and flies, the water with the numerous varieties of fish, and the very earth with reptiles of so many sorts ; all whose ways of living would be to us incredible, did not daily experience teach us; why then should we think it strange that the prodigious mass of matter, of which this globe consists, should be capable of some other im. provements, than barely to serve to support its surface? Why may not we rather suppose that the exceeding small quantity of solid matter, in respect of the fluid ether, is so disposed by the Almighty wisdom, as to yield as great a surface for the use of living creatures, as can consist with the conveniency and security of the whole?

But still it may be said, that without light there can be no living, and therefore all this apparatus of our inward globes must be use. less : to this I answer, that there are many ways of producing light, which we are wholly ignorant of; the medium itself may be always luminous, after the manner of our iynes fatui. The concave arches may in several places shine with such a substance, as invests the surface of the sun; nor can we, without a boldoess unbecoming a philosopher, adventure to assert the impossibility of peculiar lumi. naries below, of which we have no sort of idea.

Lastly, to explain yet farther what I mean, let us suppose our own globe to consist of four different circles: that the surface of VOL. IV.

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the earth is represented by the outward circle, and that the three inner circles are made nearly proportionable to the magnitudes of the planets Venus, Mars, and Mercury, all which may be included within this globe of the earth, and all the arches be more than suffi. ciently strong to bear their weight. The concave of each arch, which is shaded differently from the rest, we may suppose to be made up of magnetical matter; and the whole to turn about the same common axis ; only with this difference, that the outer sphere still moves somewhat faster than the inner. Thus, the diameter of the earth being about 8000 English miles, I allow 500 miles for the thickness of its shell, and another space of 500 miles for a medium between, capable of an immense atmosphere for the use of the globe of Venus. Venus again I give a shell of the same thickness, and leave as great a space between her concave and Mars; so likewise from Mars to Mercury, which latter ball we will suppose solid, and about 2000 miles diameter.

Since this was written, a discovery I have made in the celestial motions, seems to render a farther account of the use of the cavity of the earth, viz. To diminish its specific gravity in respect of the moon: for I think I can demonstrate, that the opposition of the ether to the motions of the planets, in long time becomes sensible; and consequently the greater body must receive a less opposition than the smaller, unless the specific gravity of the smaller do pro. portionably exceed that of the greater, in which case only they can move together; so that the cavity I assigu in the earth Day well serve to adjust its weight to that of the moon; for otherwise the earth would leave the moon behind it, and she become another primary planet.

[Phil. Trans, 1692

SECTION III.

Magnetical experiments.

1. By Mr. Sellers

He adds,

On magnetic needles. MR. Sellers states, that he had often made trial with many needles, touching them on each hemisphere of the stone, in all variety of ways he could imagine, to find if it were possible, by that means, to cause any of those needles to vary in its direction: but that he always found the contrary, all of them conforming to the magnetical meridian, and standing north and south, as other needles that were touched on the very pole of the stone. that some of these experiments he tried in London, when there was no variation known.

That on frequent trials of touching needles with different load. stones of several magnitudes, as also of different virtue, the Deedles touched gave all of them the same directions. This he thinks is confirmed by all the needles, and sea compasses, made in several parts of the world, and consequently touched on several stones of different countries, yet all agreeing in this magnetical harmony, that they all give the same directions. That having sometimes drawn a needle only over the pole of the stone, within the sphere of its virtue, without touching the stone, it has received the same directive quality from the stone as if it had been really touched on the stone itself, though not altogether so strong as if it had touched the stone. Again, that having touched needles on the stone with faint strokes, and other needles with stronger, all these needles received the same effect from the stone, both for strength and direction; he conceiving that it is not the fainter or stronger touches on the stone, nor the multiplicity of strokes, that varies the needle's strength or direction; but that the nature of the steel whereof the needle is made, and the temper that is given thereunto, cause different effects as to the strength it receives from the stone ; himself having tried all sorts of steel that he could pos. sibly procure, and all the different tempers he could imagine, for

* This seems to be the first potice of making artificial magnets. Mr. Sellers is probably the person of the same name who was the author of Practical Navigation, in 1669.

the most powerful receiving and retaining the virtue from the load. stone ; he also affirms that he has fully satisfied himself that he can infuse such virtue into a piece of steel, that it shall take up a piece of iron of two ounces weight or more ; and give also to a needle the virtue of conforming to the magnetical meridian, without the help of a loadstone or any thing else that has received virtue therefrom.

[Phil. Trans. Abr. 1667.

2. By Mr. (afterwards Dr.) Gowan Knight ; shewn before the

Royal Society, November 15, 1774*. Mr. Knight, of Magdalen College, Oxford, being introduced to a meeting of the Royal Society on Thursday the 15th of Novem. ber, 1744, produced, before the gentlemen there present, several curious artificial magnets contrived by himself; some of which consisted of plain bars of steel naked, and others of bars or blocks of the same substance, armed with iron after the common manner of natural loadstones : but as he was apprehensive the trials he had before made of the weights these magnets were respectively capable of lifting could hardly be repeated with sufficient exactness, and advantage before so large a company, he desired to refer himself, for those particulars, to what the president of the Society bad seen at his lodgings on Wednesday the 7th, and on Tuesday the 13th of the same month of November.

On which the president acquainted the company, that he had lately been several times at Mr. Knight's lodgings, where he had seen many experiments made with his artificial magnets; and that, particularly on the days abovementioned, he had been present, and had taken minutes of the following trials then made by that gentleman, by which it appeared, that

A small eight.cornered bar of steel, of the length of 7-10th inches, and about half an ounce Troy weight, lifted by one of its ends about eleven of the same ounces.

That another plain bar of steel, of a parallelopiped form, of the length of 5 9-10th inches, the breadth 4.16ths, and the thickness

* There is another paper containing an additional series of experiment on the same subject, made by the same experimentists, contained in vol. xliv. year 1747, of the Transactions; but it is not much more than an expansion of those presented above.

EDITOR

2.100hs of an inch, weighing 2 oz. 84 dwt. lifted by one of its ends twenty Troy ounces.

That a steel bar, almost of the same form as the last, but only four inches in length, capped or armed with iron at each end, cramped with silver, and weighing all together 1 oz. 14 dwt. lifted by the feet of the armour full 4 lb. Troy.

That a single block of steel of a parallelopiped form, almost four inches long, 1 2.10th inches in height, and 4-10ths of an inch in thickness, armed with iron, cramped with brass, suspended by a ring of the same, and weighing all together 14 oz. 1 dwt. lifted by the feet of the armour 14 lb. 24 oz. Troy weight.

That a compound artificial magnet was also tried, consisting of twelve bars of steel armed, and that it was found to lift by the feet of the armour, as the last, 23 lb. Troy, 2į oz.

The twelve bars, composing this last magnet, were each a little more than four inches long, 3.10ths of an inch in breadth, and 16.100ths of the same in depth, weighing one with another about 25 dwt. each. They were all placed one on another, so as to make together one paralellopiped body, of the common length and breadth of the several bars, but of the height of near two inches, being the sum of the respective thicknesses of all the bars taken together : and this paralellopiped body, being cramped with brass, and fitted with a handle of the same metal, was armed at the two ends that were made up of the common extremities of all the bars, with two substantial pieces of iron, after the common manner of arming natural loadstones, the whole frame weighing together about twenty ounces Troy.

Besides these, the president made also the following report of some trials he had seen made at the same time of the effects of an art Mr. Knight is master of, by which he can improve or increase the lifting powers of natural loadstones.

He carried with him, on Wednesday the 7th of November, a small armed loadstone belonging to an acquaintance, which weighed, with its armour, 7 dwt. 14 gr.; but which, being reputed but of an ungenerous nature, took up, and with some difficulty, barziy two ounces. Mr. Knight took it into his study, and returning it in about a minute, it then took up more than four ounces with ease : but, on his saying it would still gain some more strength, by remaining with him some time, it was left till the 13th, wüten it

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