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"constant force, it can obtain but a certain de

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gree of velocity. For, as the resistance in

creases with the velocity, but in a higher proportion, namely, as the squares, it is plain "that the resistance at a certain period of the ac"celeration will become equal to the constantly

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acting force; after which the body will pro"ceed uniformly, and the constantly acting force "will be employed in overcoming that resist

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ance. On this account it is, that bodies that "sink in water, or any other fluids, by the force "of gravity, soon acquire their utmost velocity, "and afterwards proceed uniformly. And in like

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manner, a ship, when it first gets under way, "proceeds with an accelerated velocity, till the "resistence of the water becomes in equilibrio "with the action of the wind on its sails, but "afterwards proceeds uniformly, the force of "the wind being entirely employed in over"coming that resistance*.*

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That the whole of this reasoning is founded upon that false speculative system of mathematics, which some speculative pervertor of the truth has invented for the purpose of deceiving mankind, in order that he might thereby be enabled to lead them into the paths of error, is

*See Nicholson's Introduction, Vol. 2d. Pages 25 and 26.

obvious from the following passage, in which this gentleman says:

"In mathematical strictness, it is not true, "that a body in these circumstances ever arrives "at uniformity of motion, for the approach of the "resistance to an equality with the impelling "force is represented by a converging series, the "number of whose terms is infinite, and their sum in any finite time is less than the impel"ling force; but the latter terms soon become "too small to be of any physical consequence*."

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Mr. Leslie, in the passage last quoted from his book, tells us, that this converging series which Mr. Nicholson here alludes to, and we may well suppose their pretended symtote lines also, which they tell us are continually approaching towards each other, but which they say can never meet together in any point, although they should be extended through eternity, are deduced from this celebrated principle of the conservatio virium vivarum. We must acknowledge, that these incomprehensible effects are well worthy of such an imaginary undefinable parent.

It requires but a very small exercise of these rational faculties which the Creator has bestow

Nicholson's Introduction, Vol. 2d. Page 26.

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ed upon man, to perceive that this speculative nonsense is altogether false. It is perfectly obvious to the common understanding of mankind, that if any two lines are drawn so as to approach towards each other, let that approach be ever so small, though it should not exceed the thousand part of an inch in a thousand miles, yet these two lines still continuing to approach each other in the same proportion, must necessarily at some period, meet together in the same point.

When Euclid undertook to instruct mankind in the knowledge and use of geometry, he endeavoured to convey this knowledge to their minds by sensible figures. But these speculative philosophers have inverted this sensible mode of instruction which Euclid adopted, and which every true philosopher must necessarily adopt, and they pretend to convey to their pupils a knowledge of natural and visible objects by things that are unseen, and which are altogether incomprehensible to the mind of

man.

The great end and object of that science which is termed natural philosophy, is, as the Apostle expresses it, to obtain a knowledge of the invisible things of God from the foundation of

the world, by the contemplation of those visible objects which he has created. But these gentlemen endeavour to make us believe, that we can only acquire a perfect knowledge of those visible objects, by means of things which like their pretended converging series of infinite terms, is altogether invisible and incomprehensible. It is, however, very obvious that it is impossible for men to acquire any certain knowledge either of God himself, or of his works, by such a ridiculous mode of instruction. But the real fact is, as was before obversed, these speculative philosophers would wish to persuade us to renounce the testimony of our own senses, and of our own understanding, and believe implicitly in those speculative, irrational, and impious opinions, which they endeavour to impose upon

us.

Mr. Nicholson, like his brother philosopher, Mr. Leslie, has flatly and pointedly contradicted himself in these two passages before quoted. In the first, he says, "That bodies descending "through fluids by the force of gravity soon acquire their utmost velocity, and afterwards

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proceed uniformly." In the next passage, he tells us as positively, that what he had told us before, is not true; and that a body in these cir

cumstances, never arrives at an uniformity of

motion.

But let us quit this ridiculous irrational method of philosophizing, and employ those senses and those faculties which the Creator has been pleased to bestow upon us, for the purpose of enabling us to acquire a knowledge of truth, and prove, by the testimony of those senses, that this celebrated principle, this conservatio virium vivarum is a false principle, and that the motion of bodies descending through fluids is not ob structed in proportion to the squares of their velocity, or in any other way than that of the simple, relative specific gravity of the body, to that of the fluid through which it moves; and that bodies descending through fluids do continually accelerate in their motions.

In order to show that this is true, let us in round numbers suppose the specific gravity of

the air in which we breathe to be

That of water

And that of lead

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0,001

1.000 11.000

It is a simple and universally acknowledged axiom in philosophy, that solid bodies, whose specific gravity is less than that of the fluid in which they may be immersed, cannot sink or descend to the bottom of that fluid, but will be

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