portant truths are concealed; and which none but the most learned are able to discover.

By this false system of mathematics, which is now almost universally taught in our schools, the minds of youth are led into the paths of error in the very outset of their inquiry after truth; and they are thereby made to spend some years of the most precious part of their lives, in vainly searching after that pretended knowledge which having no existence in nature, is no where to be found.

Of this perversion of mathematical truths, and of the perversion of the natural use of language, I shall now give a few examples from Mr. Leslie's Inquiry into the Nature and Propagation of Heat.

Mr. Leslie pretends to found his reasoning in this Enquiry upon certain experiments which he had previously made, and which are detailed in the beginning of his book.

Every experiment, it must be acknowledged, is a direct appeal to the senses, and to the common understandings of mankind. And the result of every experiment, if it has been properly conducted, must either be an obvious truth, or axiom, or it is nothing. But we too frequently find speculative philosophers spending their

time, and multiplying experiment upon experiment, not for the purpose of obtaining a knowledge of the truth, but for the purpose of confusing the minds of other men; and for the purpose of supporting some speculative opinion which they themselves have previously entertained. It is not difficult for such men to conduct their experiments in such a way as to deceive superficial observers, and make them. believe that the result of the experiment is a direct confirmation of their own speculative opinion. It is therefore necessary, before we give our assent to the apparent result of any experiment, that we should be previously convinced that the experiment itself has been properly and rationally conducted. But it gene

rally happens, when such men attempt to multiply experiment upon experiment, and to change the same simple experiment into three or four different shapes, in order to deceive, that they themselves are caught in that very snare which they are laying for other men, and alter the truth without seeming to be sensible of it. In these cases it uniformly happens, that these men, in their reasoning upon their experiments, flatly and positively contradict those very truths

which they had unguardedly uttered immediately before.

How far these observations do apply to Mr. Leslie's conduct, will best appear from the account which he himself gives us of those experiments, which will afterwards become the subject of our observations.

That Mr. Leslie did set out in this Inquiry, with a preconceived speculative opinion of his own respecting the nature of heat, he himself tells us very plainly in the preface to his book, where he says, "Reflection had long taught me "to consider the communication of heat among "insulated bodies, as performed only by the me❝dium of the intervening air. This opinion I "now put beyond dispute." And although he does not expressly say so, it will appear very evident afterwards, that he set out also with another speculative opinion, viz. that the rays of heat proceeding from a heated body, do not, like those of light radiate in all directions from the centre of the body; and that they are not, like light equally diffused through the adjoining space. And it will appear, from a careful examination of a few of those experiments which he relates, that he has uniformly endeavoured C

to support these speculative opinions, by a manifest perversion of the truth.

But in order to render the observations which I have to make upon these experiments objects of sense, and to be thereby enabled to convey the truth of them more perfectly to the mind of the reader, I must, in the first place, delineate the situation of the different instruments employed by him in these experiments, as described by himself.

Let the lines A B C D (see plate 1.) represent the table upon which the experiments were made; the small segment of the circle E the reflector, 12 inches in diameter; F the thermometer, placed in the focus of the reflector; G the canister, of four inches square, placed at ten times its own breadth from the reflector, as directed in the 20th experiment, and in the centre of the circle E HIK.

We shall now proceed to examine

EXPERIMENT I.

Which Mr. Leslie describes as follows:"Paint one side of the canister with lamp-black; "coat another with writing-paper, and cover a "third side with a pane of crown glass. Thus prepared, dispose the apparatus for action;

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turn the black side of the canister to front the "reflector, and fill it with boiling water. The "liquor of the differential thermometer will rise ❝ to 100 degrees. Bring the papered side into "the same position, a similar effect, though ra"ther smaller, will be produced, equal to 98 "degrees. The vitreous surface will betray a "sensible diminution, its action amounting to "about 90 degrees.

"Thus blacking, paper, and glass, constitute "the same class of substances, whose effects, tho' somewhat different, are all very considerable."

EXPERIMENT II.

"Things being still in the same situation, di"rect the bright side of the canister to face the "reflector, and the effect on the focal ball will "be observed to suffer a very remarkable change, "the coloured liquor quickly sinking to 12 de"grees: but any side of the canister, covered "with tinfoil, and brought into the due position, "will manifest precisely the same action.

"Thus, in its affection to heat, is tin radically "distinguished from blacking, or paper, or even "glass, since, compared with them, it exhibits "only about the eighth part of the energy."

These two experiments, in so far as they have