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puscles, or atoms, almost infinitely small, are in perpetual motion : that every corpuscle has its determined direction, and moves for ever in a straight line, with a velocity far exceeding that of light. It is evident that the directions of these corpuscles may be so various, they may be themselves so small, and their ve. locity so great, that though they follow one another at vast distances, and leave space, in reality, almost empty, yet may they abound every where in such a manner, that in a portion of time almost infinitely small, a great number of them may pass through every point of space whatsoever. . On whatever point of space, therefore, our attention is fixed, we may consider it as a centre, to which the motions of an infinite number of atoms are referred, either diverging from it, or converging to it.

This constitution of what Le Sage calls the gravific fluid being conceived, suppose a solid body to be plunged into it, of any figure whatsoever, larger than one of the corpuscles, and, in some degree, if not wholly, impervious to those corpuscles. This body will remain at rest, or at least without any progessive motion, the impulses from the corpuscles that strike against it being equal in opposite directions. It may oscillate a little backwards and forwards, but will not be forced from its place.

Now let there be plunged into the gravific fluid another body of any figure, and at any distance from the first. These two bodies will immediately begin to move toward one another: for the one serving to protect the other from a certain quantity of the impulsion of the corpuscles, the currents thus left without opposition necessarily produce their effect, and impel the bodies toward one another. Their motion toward one another will be continually accelerated; and the force producing that acceleration will increase in proportion as one body stops more of the currents from falling on the other; that is, nearly as the squares of the distances diminish. · Again, if the solid particles of which the bodies are made up be impenetrable to the gravific corpuscles, but the bodies themselves, on account of their

porosity, permeable by them in a certain degree, the number of corpuscles that are stopped by each of the. bodies will be, cæteris paribus, proportional to the number of solid particles, that is, to the quantities of matter within the bodies; and hence, in general, the force urging the bodies towards one another will be directly as their masses, and inversely as the squares of their distances. Thus, by mechanical action, the. Newtonian law of gravitation is explained in all its parts.

The principal objection against this theory is grounded on the vast expense of matter required to uphold the existence of the gravific fluid. "No pare ticle of that fluid returns to its place, or ever passes a second time through the same point of space. A con. stant supply of new particles is therefore necessary, as all those that are contained within the limits of the sensible universe, at any instant, must be replaced long before they have entirely escaped from it, and gone forth to traverse for ever the deserts of uninhabited ex. tension. The imagination is terrified at this constant exertion of what cannot be considered as less than creative power, employed in producing existences,, that for a limited time are to be useful, and through all the rest of infinite duration are to serve no pur. pose whatsoever! The difficulty is indeed great, and we are still brought in sight of the cause to which all others are subordinate, the CAUSE which-all rational systems must acknowledge, and can only differ about the point where its immediate action begins, and be. yond which secondary causes cannot be traced..

Boscovich's system does not, strictly speaking, as sign the cause of gravity, but only generalizes the facts : concerning the actions of bodies on one another, and i reduces them all to one..

M. PHOSTON.

OBSERVATIONS ON THE DRY ROT. I was led to pay much attention to the query respecte: ing what is commonly called the. Dry Rot in Wood, , proposed in the first. number of the Enquirer, from the circumstance of having injudiciously purchased a house, in which the timber was found to be much decayed by this disease; and however much I was gratified by the remarks in the 2d and 3d Numbers, I by no means consider those remarks as conclusive on the subject, and request the indulgence 6f submitting my own observations on this destructive phenomena.

I would just observe, by the way, that in the fourteenth Chapter of Leviticus there is an account of the leprosy of a house Query, might not this be the dry rot?

Unquestionably the best mode of acquiring an exact knowledge of this distemper would be

First, To study the general nature of the soil in which houses affected with the dry rot are built. · Secondly, The adventitious or accidental causes of the dry rot.

Thirdly, The effect of the dry rot on different kinds of stone, and other hard inaterials used in building.

Fourthly, The effect of the dry rot on timber, and the various kinds of timber most readily affected by it.

To these might be added, miscellaneous observations, containing an account of the peculiar effects of the dry Tot in certain situations; and of the means used, with or without success, for preventing or curing timber affected with the distemper.

It is not without the greatest diffidence that I mention this arrangement, from a consciousness of the very imperfect manner in which I have been able to execute my own design; but many allowances will be made for the first essay on any subject.

The result of my observations, and the circumstances thereon attending is, that the cause of the rot in timber is derived from the ground; that the ground which produces this distemper is always damp; and that the stone most commonly used for paving floors does not interrupt the cause of the rot. My ideas of the nature and cause of this vegetable disease are, that although it is called by the general name of rot, or dry rot, it may perhaps be discovered at some future time, that there are many varieties both of the distemper and its causes. The prevailing opinion is well known, that it is a species of vegetation, but without deciding with sufficient accuracy upon the primary or predisposing cause, or what the nature of that vegetation is. Some have supposed it to be of the animal kind, and probably because of the observation that places in which snails have been decayed, do not fail to produce mushrooms; which has led, if I mistake not, to a doubt whether mushrooms were of the animal or vegetable tribe; or because no man has yet been able to distinguish where the animal kingdom ends and the vegetable begins; or that no language can exactly define an animal from a vegetable, though every one can clearly distinguish them in his own mind. The first effect which earth capable of producing the rot shows, is its being continually moister than healthy earth, but the moisture is not the substance of the disease, no more than the matter of the small-pox is the infecting principle, which is of the most subtle nature, and only mixed or enveloped with the matter as its vehicle; so the moisture of earth impregnated with the rot, does not seem to be the prin. ciple of the rot, but is merely the vehicle or conductor of the miasmata or primary principles of that distemper. It would be worth while to try ground which produces the rot, as well as wood affected by it, with electric experiments, whether it abounds with, or is deficient in, electric fire; but there is a multiplicity of things which an ingenious man, who could spare time, might try, for the purposes of investigating either the cause or the effect of the rot; and if he had the saga. city or good fortune to discover a certain method of preventing it, he would do a very essential service to society.

A number of means have been proposed for the prevention of the disease in question, by applications to the timber itself; but I think we should be very cautious in applying substances to suspend the operation of the native principles, lest we introduce other principles of decay. It is probable, that keeping timber a sufficient length of time before it is employed, is the most advantageous method of preparing it. Norwich, Jan, 16, 1812,

J, KEMP

REPLY TO PLINY'S LETTER TO LICINIUS.

(See ENQUIRER, Vol. II. p. 79.) The most probable cause of this curious phenomenon is, that some pipe or hollow in the earth, bent in the form of a syphon, communicates with the bottom of the fountain; and proceeding thence towards the Larian lake, opens at some place lower than the bottom of the fountain. Admitting this to be the case, when the water in the fountain has risen above the bend of the pipe, it will flow through into the lake; and will continue flowing until the fountain be emptied; it will then cease to flow, until the fountain be again filled above the bend of the pipe, when it will again begin to flow, and so on alternately; hence the cause of the phenomenon is evident. Burstwick, March 16, 1812.

W. ALLEN.

· TO THE EDITORS OF THE ENQUIRER. I SEND you the following extract from Encyclopædia Britannica, in answer to ContriBUTOR.

« Certain springs pr fountains are observed to have periods of repletion and scantiness, or seem to ebb and flow at regular intervals; and some of these periods are of a complicated nature. Thus a well will have several returns of high and low water, the difference of which gradually increases to a maximum, and then diminishes, just as we observe in the ocean. A very ingenious and probable explanation of this has been given in No. 424 of the Philosophical Transactions by. Mr. Atwell as follows:

Let ABCD represent a cavern, into which water is brought by the subterraneous passage OT. Let it have an outlet MNP of a crooked form, with its highest part N considerably raised above the bottom of the cavern, and thence sloping downwards into lower ground, and terminating in an open well at P. Let the dimensions of this canal be such that it will disa charge much more water than is. supplied by TO.

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