ing a prodigious spherical mass of loadstone in its center; and that the variations of the needle may be occasioned by the variations which the magnetic substance undergoes by earthquakes, and other subterraneous phænomena. * But this can never be ascertained; and as an hypothesis, it is attended with many difficulties. We shall, therefore, abide by the more simple explanation; and shall only just remark, that the application which is made of the loadstone to navigation; the incessant occasion which sailors have to consult it as a guide; the visible language which it speaks, and which makes it a supplement to the language of the heavens, is most wonderful and sublime.

LETTER XXXVII.

FROM all that has thus far appeared; from the general texture of bodies; and from the penetrating energies of the several elementary fluids, it would seem to be demonstrable, that there is no substance perfectly solid in nature. Even gold itself, the heaviest of all substances hitherto known, excepting platina, is perforated with invisible pores, to the amount of one half of its bulk, as has been conjectured by Newton. Hence we may form some judgment of the vacuities of other bodies: the internal structure of which, indeed, may be compared to a spunge, though the apertures cannot in general be perceived.*

Where then is the impenetrability of matter? Father Boscovich denies there is any such thing; and though he does not go quite so far as to expel all body out of the universe, he thus robs it of one of its most substantial qualities. The same hypothesis occurred to Mr. Mitchell. Matter, according to these philosophers, is an aggregate

* Bergman.

aggregate of physical points, endued with
powers
of attraction and repulsion, taking place
at different distances; that is, it is surrounded
with various spheres of attraction and repulsion,
in the same manner as solid matter is generally
supposed to be. If the degree of velocity there-
fore, or the momentum of any body in motion,
be sufficiently great to overcome any of those
powers of repulsion it may meet with in
any
other body that opposes its passage, it will find
no difficulty in making its way through that
body; and this even without moving the parti-
cles of that other body out of their place. On
these grounds, the solidity or impenetrability,
and consequently the vis inertia of matter,
must be supposed founded on superficial ap-

pearances.

But Mr. Mitchell, in his Treatise on Earthquakes, is still more explicit. He says, the compressibility and elasticity of the earth, are qualities which do not shew themselves in any great degree, in common instances. On this account, few people are aware of the great extent of them. In some measure, however, they may be collected from the vibration of the walls of houses, occasioned by the passing of carriages in the streets next to them. Another

instance

instance may be taken from the vibration of steeples, occasioned by the ringing of bells, or gusts of wind: not only spires are moved very considerably by this means, but, even strong towers are made to vibrate several inches, without any disjointing of the mortar, or rubbing of the stones one against another. Now this could not happen, says he, without a considerable degree of compressibility, and elasticity, in the materials of which they are composed.

Of this, however, we shall afterwards have occasion to treat more particularly. All the parts of nature are indisputably connected; air, water, carths, plants, minerals, animated and inanimated substances, are all linked together by some correspondence between causes and effects every being in the universe is related to some other, and operated upon by it; and thus there cannot be a doubt but that nature is in continual action, and that her springs are as powerful under our feet, as they are over our heads. But, though the characters of nature are thus legible, they are not, as you perceive, so plain, as to enable those who run to read. Caution and discrimination must guard the inquirer. We must not attempt to fly, when we can scarcely pretend to creep. In considering a complex

a complex question, we must examine every distinct ingredient in the composition; and reduce every thing to its elementary simplicity. The condition of the human understanding, binds us to a strict law, and to very narrow limits. But unfortunately, it is an easier and a readier way, to consult one's own ideasand here I am very far from alluding to the two very respectable philosophers I have just mentioned than to attend to the operations of nature. Phænomena, indeed, accumulate on phænomena, but the eager man feels them only in the extent of his own feeble powers of explanation. Beyond the measure of his own understanding, he scarcely deigns to cast a consideration. Ignorant of the cause, he yet would generalize as the Almighty Fabricator of the Universe. How rash and hazardous the folly! In the disposition to sound philosophy, how infinitely more wise, to confess the small extent of our acquisitions; and soberly to proceed from the principle of, I know nothing, to the more enlightened point of experiment, and certain observation! What awe, in the contemplation of the energies and the laws of material and immaterial existence; of the generation and the destruction of those things, that appearing merely for an instant on the stage of