Mr. Leslie, having, as he vainly imagined,. established his own speculative opinions respecting the nature and propagation of heat, by that perversion of truth which is so conspicuously displayed in the account he gives of his different experiments; he proceeds in the 8th chapter, to rear a building upon this false foundation. But seeing that the foundation is altogether visionaty, we may well believe that the superstructure which he pretends to raise upon it, must be visionary also.

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The whole of this chapter is, indeed, so perfect an example of the false construction of language, such a complete mixture of truth and falsehood, of speculative opinions, and speculative mathematical nonsense, and so profusely embellished with learned names and technical terms, that no human being can pretend to understand it, or discover what object the author has in view. But he at last assumes to himself the appearance of an angel of light, and steps forth out of this dark cloud, to enlighten our darkened understandings. He says, "The whole scope of this reasoning, it will be perceived, is in direct contradiction to the noted axiom of "the schools, that nothing acts where it is not. "But I would observe, that all axioms are merely

"the simple conclusions drawn a priori from "familiar experience; that, however fitted for the "ordinary business of life, they are useless and " even prejudicial in philosophy; and, that being "derived from loose and superficial views, they "often require restriction, and are liable to inaccuracy. In matters of science, the general "opinion of mankind, termed common sense, is

always a very suspicious standard of appeal. "If a body acted only within itself, it is clear, "that the force could never be transraitted; there' "would be no communication, no sympathy "with the rest of the universe. In vain shall "we have recourse to the agency of invisible in"termedia: the interposing of successive stations

may divide, but will not annihilate distance; "and, after torturing our imagination, the same • difficulty still recoils upon us.'

"It is a remarkable and instructive fact in "the history of philosophy, that impulsion "should have been at one period the only force "that was admitted. The motion of a falling

stone was certainly not less familiar to the senses, than that of a stone which is thrown 1; "but in the latter case, the contact of the hand

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was observed to precede the flight of the pro“jectile, and this circumstance seemed to fill up

* the void, and satisfy the imagination. Gravi"tation sounded like an occult quality: it was 66 necessary to assign some mechanical cause; and "if there were no visible impulses to account for "the weight of the body, might not that office "be performed by some invisible agent? such 66 was the sway of metaphysical prejudice, that 66 even Newton forgetting his usual caution, suf"fered himself to be born along. In an evil " hour he threw out those hasty conjectures con"cerning æther, which have since proved so "alluring to superficial thinkers, and which have "in avery sensible degree impeded the progress "of genuine science. So far from resolving "weight or pressure into impulse, we have seen "that the very reverse takes place, and that im"pulse itself is only a modification of pressure. "This statement has already some distinguished " adherents, and must in time become the re"ceived opinion. opinion. Science has experienced "much obstruction, from the mysterious notions "long entertained concerning causation."

Here we have a pretty clear declaration under Mr. Leslie's own hand, of the great object which he proposed to gain by that manifest perversion of truth which appears so clearly throughout the whole of this inquiry. The

first great object appears to be, to overtum the established opinions of mankind; and for this purpose, he endeavours to persuade us, to trust no longer in the testimonyi of those senses, and in that rational understanding which the Almighty has been graciously pleased to bestow upon us, for the purpose of enabling us to acquire a knowledge of truth.

In this declaration of his sentiments, the cloven foot appears. This we find is the means which the great deceiver of mankind, has employed to seduce them from their allegiance to God; and to bring them under bondage to himself, and to his ministers.

The inhabitants of every nation who have been seduced to worship idols, must of necessity have renounced the testimony of their own senses; and have given up the exercise of their own natural understanding, into the hands of the priests who officiated. at their altars, before they could be brought to believe that' these dumb idols whom they were taught to worship, had power to confer blessings, or inflict punishments upon mankind. It is also well known, that every member of the church of Rome, is expressly required to give up the exercise of his own natural understanding in

matters of religion, and to believe only as mother church believes, or, in other words, to obey implicitly the arbitrary will of the Pope.

It is exceedingly obvious that this learned author is either ignorant of the real meaning of the term axiom, or wishes to pervert and obscure that knowledge in the minds of other men. I have before observed, that natural axioms, or those simple truths upon which that science termed natural philosophy is founded, are those truths respecting the existence of external objects, the knowledge of which is instantaneously conveyed to the mind by the organs of sense, such as a man, a horse, a house, a tree, &c. The proper exercise of that common understanding, or of those rational faculties which the Creator has bestowed upon men, consists in employing this knowledge, which has been conveyed to the mind by the organs of sense, to its proper use. For example, if I should in the course of my travels through the country, see a person lying upon the side of the road, in the same situation as the man in the gospel who fell among thieves; stripped like him of his raiment; wounded, and bleeding, and half dead. That he is in this distressed situation, is to me an axiom ; my own senses bearing witness that H