1.  I go on to some articles of natural philosophy, where I shall endeavour to show the conformity there is between the ancients, and some of our most celebrated philosophers. It is evident, that the causes of thunder, earthquakes, the attractive force of the loadstone, the ebbing and flowing of the sea, and the return of rivers to their source were not hid from the former: nor was it their fault, that the sentiments they so long ago held on these subjects, were either not adopted, or not till very lately. It ought not to be objected here, that the diversity of opinions among them was not so great, that it was difficult to determine which to choose: unless at the same time, it be acknowledged, that the same holds true with respect to the equal variety that reigns at present among us. It is not long ago, that two or three different sets of notions were raised up against those of Sir Isaac Newton, respecting colours, but that did not impede the triumph of his system, nor strip him of the glory of having proposed, what, beyond all others, was most just and solid.

2.  The moderns are divided into two opinions as to what occasions thunder; some of them assigning the cause of it to inflamed exhalations, rending the clouds wherein they are confined; others ascribing it to the shock that happens between two or more clouds, when those that are higher and more condensed, fall upon those that are lower, with so much force as suddenly to expel the Intermediate air, which vigorously expanding itself, in order to occupy its former space, puts all the exterior air in commotion, producing those reiterated claps which we call thunder. I stop not to examine a third theory, which makes the matter productive of thunder, the same with that which is the cause of electricity; for though it be the most probable of any, yet the truth of it is still contested.

3.  Of those two sentiments of the ancients, which have been adopt ed by our moderns, the latter belongs to Aristotle, who says, that thunder is caused by a dry exhalation, which falling upon a humid cloud, and violently endeavouring to force a passage for itself, produces the peals which we hear. And Anaxagoras refers it to the same cause. All the other passages, which occur in such abundance among the ancients, respecting the formation of thunder, evidently con-thin the reasonings of the Newtonians, and sometimes join together the two sentiments which divide the moderns.

4.  Leucippus held, that thunder proceeded from a fiery exhalation, which enclosed in a cloud, burst it asunder, and forced its way through. Democritus asserts, that it is the effect of a mingled collection of various volatile particles, which impel downwards the cloud which contains them, till by the rapidity of their motion, they set themselves and it on fire. Seneca ascribes it to a dry sulphureous exhalation arising out of the earth, which he calls the aliment of lightning; and which, becoming more and more subtilized in its ascent, at last takes fire in the air, and produces a violent eruption.

5.  The Stoics distinguish two things in thunder, the lightning and the noise. According to them, thunder was occasioned by the shock of clouds ; and lightning was the combustion of the volatile parts of the cloud, set on. fire by the shock: and Chrysippus taught, that lightning was the result of clouds being set on fire by winds, which dashed them one against another; and that thunder was the noise produced by that re-encounter: he added, that these effects were coincident ; our perception of the lightning before the thunder-clap, being entirely owing to our sight being quicker than our hearing.

6.  There is but one opinion respecting the cause of earthquakes, which deserves any notice; and it is that of the Cartesians, Newtonians, and all our other able naturalists, They ascribe it to the earth’s being filled with cavities of a vast extent, containing in them an immense quantity of thick exhalations, of a fuliginous substance, resembling the smoke of an extinguished candle, which being easily inflammable, arid by their agitation catching fire, rarely and heat the central condensed air of the cavern to such a degree, that finding no vent to issue it, it bursts its enclosements ; and in doing this, shakes the earth all around with dreadful percussions, producing all the other effects which naturally follow.

7.   The same reason is given by Aristotle and Seneca, in assigning the cause of such dreadful events. The former, after refuting those who ascribed earthquakes to the earth itself, or the water it contains, subjoins his own opinion, “that they were occasioned by the efforts of the internal air in dislodging itself from the bowels of the earth ;“ and he observes, that “on the approach of an earthquake, the weather is generally serene, because that sort of air which occasions commotions in the atmosphere, is at that time pent up in the entrails of the earth.”

8.  Seneca is still more precise ; we might take him for a naturalist of the present times. He supposes, that “the earth hides in its bosom many subterraneous fires which uniting their flames, necessarily put into fervid motion the congregated vapours of its cells, which finding no immediate outlet, exert their utmost powers, till at last they force a way through whatever opposes them.” He says also, that if the vapours be too weak to burst the barriers which retain them, all their efforts end in weak shocks, and hollow murmurs, without any fatal consequence..

9.  Of all the solutions that ever were attempted to be given of the ebbing and flowing of the sea, the most simple and ingenious, is, that of Kepler and Sir Isaac Newton. It is founded on this hypothesis, that the moon attracts the waters of the sea, diminishing the weight of all those parts of it over whose zenith it comes, and increasing the weight of the collateral parts, so that the parts directly opposite to the moon, and under it in the same hemisphere, must become more elevated than the rest. According to this system, the action of the sun concurs with that of the moon, in occasioning the tides; which are higher or lower respectively, according to the situation of those two luminaries, which, when in conjunction, act in concert, raising the tides to the greatest height; and when in opposition, produce nearly the same effect, in swelling the waters of the opposite hemispheres: but when in quadrature, suspend each other’s force, so as to act only by the difference of their powers: and thus the tides vary, according to the different positions of those luminaries.

*would be more philosophical to say, the moon attracts the atmosphere, and the waters naturally conform themselves to its figure, or to its various degree! of pressure. See Note to page 451, vol. I.

  10.  Pliny’s account agrees with this. That great naturalist. maintained, “ that the sun and moon had a reciprocal share in causing the tides ;“ and after a course of observations for many years, remarks that the moon acted most forcibly upon the waters, when it nearest to the earth, but that the effect was not immediately perceived by us, but at such an interval as may well take place between the actions of celestial causes, and the discernible result of them on earth. He remarked also, that the waters, which are naturally inert, do swell up immediately upon the conjunction of the sun and moon; but having gradually admitted the impulse, and begun to raise themselves continue in that elevation, even after the conjunction is over.

11.   There are few things which have more engaged the attention of naturalists, and with less success, than the wonderful properties the loadstone. At all times men have hazarded a variety of conjectures, to account for the curious effects of it. Almost all have agreed in assigning this as a principal reason, that there are corpuscles of a peculiar form and energy, that continually circulate around and through, the loadstone, and a vortex of the same matter, circulating around and through the earth. Upon these suppositions, the modern philosophers have advanced, that the loadstone hath two poles, similar to those of the earth ; and that the magnetic matter which issues at one of the poles, and circulates around to enter at the other, occasions that hath pulse which brings iron to the loadstone, whose, small corpuscles have an analogy to the pores of iron, fitting them to lay hold of it, but not of other bodies. This is almost all that hath been reasonably advanced with respect to the virtue of the magnet, and all this the ancients had said before.

12.   This impulsive force, which joins iron to the loadstone, and other things to amber, was known to Plato ; though he would not call it attraction, as allowing no such cause in nature. This philosopher called the magnet, the stone of Hercules, because it subdued iron, which conquers every thing. Lucretius also knew what caused this property in the loadstone, and without doubt furnished Descartes with his explanation. He admitted, that there was a “vortex of corpuscles, or magnetic matter, which continually circulating around the load-stone, repelled the intervening air betwixt itself and the iron. The air thus repelled, the intervening space,” says that philosopher,.” became a vacuum ; and the iron, finding no resistance, approached with an impulsive force, pushed on by the air behind it.” Plutarch likewise is of the same opinion. He says, “amber attracts none of those things that are brought to it, any more than the loadstone. That stone emits a matter, which reflects the circumambient air, and thereby forms a void. That expelled air puts in motion the air before it, which making a circle returns to the void space, driving before it, towards the loadstone, the iron which it meets in its way.” He then proposes a difficulty, “ why the vortex which circulates round the loadstone, does not make its way to wood or stone, as well as iron “ He answers, like Descartes, that the pores of iron have an analogy to the particles of the vortex circulating about the loadstone, which yields them such access as they can find in no other bodies, whose pores are differently formed.

13.   It is scarce credible, that the real cause of electricity was known to the ancients, though there be indications of it in the work of Timoeus Locrensis, concerning the soul of the world, a respectable monument of ancient philosophy. It is true, that modern naturalists themselves are divided on this point, not indeed with respect to the general cause of electricity, hut with regard to the causes of the different directions of the electric matter. They do not indeed say wherein the essence of this matter consists; they only define it by its properties, and explain it by its effects; yet all own, that it is “a very subtile fluid,” residing around electric bodies, which upon being put into motion by the friction of those bodies, or any other cause, forcibly rushes into them, carrying along with it all the minute things contained in its vortex, and producing all the other effects of electricity which we perceive : now this is precisely what Tioemus says of it, in giving the reason of amber’s attracting bodies ; “ this happens,” says he, “ because there issues from the amber a subtile matter, by which it draws other bodies to itself.”

14.  The moderns are also divided in their sentiments, how it comes to pass, that rivers continually flowing into the sea, do not swell its mass of waters, so as to make it overflow its banks. One of the chief solutions of this difficulty is, that rivers return again to their source by subterraneons passages, which nature hath formed for that purpose; there being between the sea and the springs of rivers, a circulation analogous to that of blood in the human body. This explanation of the origin of rivers, and the comparison respecting their circulation, is taken from Seneca: who accounts not only for their not overflowing the bed of the ocean, by the secret passages formed for them by nature to reconduct them to their springs; but assigns this reason why, at their springs, they retain nothing of that brackishness, which they carried with them from the sea; because, says he, they are completely filtrated in that extensive circuit they make under ground, through winding paths of all dimensions, and through layers of every soil ; so that they must needs return to their source, as pure and sweet as they departed thence.

Chapter 10 - Of Ether. And the Weight and Elasticity of the Air

Chapter 10