immediately thrown up to the surface, and float upon it-for example, a piece of fir-wood in water. If a solid body of precisely the same specific gravity as a fluid, be laid upon the surface of that fluid, we know that it will sink down so far as to remove that part of the fluid which is equal to the bulk of its own body: or, in other words, it will sink down until the upper surface of the body is equal with the surface. of the fluid, and there it will femain. But if the specific gravity of the body be only a few grains heavier than that of the fluid, it will then sink to the bottom, and the motion of the body will accelerate in its descent through the fluid, exactly in proportion to the difference or ex-, cess of its own specific gravity above that of the fluid; that difference being the constantly acting force which impels the body forward in its descent.

Suppose the body A, (see plate II. No. 1.) to be a ball of lead, and the perpendicular lines B C D E to represent a space in the atmosphere precisely equal to the diameter of the ball: let us suppose that the ball has to descend through the atmosphere, from E to D, where it falls upon the surface of the earth. And let us also suppose the horizontal lines, a b, c, &c. to re

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present certain equal portions of the column of the atmosphere through which the ball has to pass, of ten, one hundred, or any number of yards each. The specific gravity of the air being 1, and that of the ball of lead 11,000; the difference of the power of these two bodies is, therefore, 10,99. The body of air through which the ball has to pass, can only oppose its descent with a force equal to 1; and the ball will overcome that opposition, with a force 10,999 times greater than that which the air possesses to oppose it. But this is not all: this difference in the specific gravity of these two bodies becomes a constantly acting force to impell the ball forward: and from this cause the velocity of the ball, and consequently its force, will be constantly and regularly increasing, in proportion to this difference between the speci-, fic gravity of the ball and that of the air through which it moves.

We know it to be an unquestionable truth, that the body of air through which the ball has to pass, cannot exert one particle of more power to obstruct the descent of the ball, than that which the Creator has bestowed upon it: and this, we know, is only one 11,000 part of the original power of the ball. These being un

questionable truths, it is obvious, that the ball cannot meet with one particle of more obstruction in its descent from r to s, than it did from a to b.

It seems, however, that our speculative philosophers would wish to make us believe, that this celebrated principle of theirs can bestow a much greater degree of power upon natural bodies, than the Creator himself has bestowed upon them; and that it has invested the atmosphere with the power of obstructing the ball of lead in its descent, with a force the velocity of the ball. principle has any existence in nature, it must be a lying spirit, and can have sprung from none other but him who is the father of lies, as I shall afterwards show.

equal to the square of But if this celebrated

The difference between the specific gravity of lead, and that of air, being so very great, and that difference being the constantly acting force which impels the ball forward in its descent, we may well suppose that the motion of the ball would, from this cause, accelerate in a geometrical, or duplicate ratio. This being supposed, the following table will show us distinctly, in the first column, the increasing velocity of the ball; in the second column, its increasing

Mr. Nicholson, in the passage quoted above, says, that The sum of the terms of the resisting fluid, in any finite time, is less than the impelling force. But is this the case? We have only carried the preceding statement to the 20th term, and the sum of the terms of the resisting power is there, in place of being less, nearly seventy times greater than the sum of the terms of the impelling force. At the 14th term, the resisting and the impelling forces approach towards an equality; but at the 15th term, it appears from the preceding statement, that this celebrated principle has invested the air with a power one-half greater than the force of the ball at the same period. If this had been true, it is obvious that the motion of the ball must have ceased before it arrived at the 15th term. For these speculative philosophers may as well endeavour to make us believe, that a bladder filled with air will sink in water, as say that the leaden ball could descend through the air, if it was really opposed by a power greater than its

own.

These speculative gentlemen would wish to make us believe that all kinds of motion in material bodies proceed from the same cause. Mr. Leslie towards the end of his 8th chapter, ex