the glass it is obvious, that the reflecting power of the tin-foil, or of the tin-plate, would be in like manner destroyed by the pane of glass, and the black coating, as described in the 10th and 11th Experiments and we accordingly find, from these experiments, that the reflecting power of the tin being thus destroyed, the glass, in the 10th Experiment, transmitted nearly the same quantity of the rays of heat through the tin-foil to the reflector, that it did in the 6th Experiment when the tin-foil was not attached to it. And we find from the 11th Experiment, that the black coating transmitted precisely the same quantity of the rays of heat through the in-plate, as the paper-screen did in the 8th Experiment.

Dr. Speculative having, as he vainly imagined, by his speculative methematical reasoning, established his own speculative opinion respecting the nature of heat, he proceeds in the fifth chapter to broach his other speculative opinion, viz, that the rays of heat proceeding from a heated body, do not radiate in all directions like the rays of light; and that they are not equally diffused through the adjoining space. Mr. Truth is therefore again set to work, to drudge through another set of Experiments, to

prove that this second speculative opinion is

also true.

In the beginning of the fifth chapter, honest Mr. Truth, by way of preface to these Experiments, which he was about to commence, recalls our recollection to those truths which he had told us in the preceding Experiments. He says, "It has been already shown, that the original

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impressions of heat and cold, are not propa"gated merely in lines perpendicular to the side "of the canister. But this," he says, may be "rendered obvious, by giving the blackened "surface of the canister, a small degree of obli

quity in regard to the axis of the reflector, "for the effect is not thereby visibly altered." But this simple relation of Truth, and this direct appeal to the testimony of our senses did not suit Dr. Speculative's purpose; and stepping forward here, he endeavours to raise some doubt in our minds, respecting the fact which honest Truth had just before uttered; for the purpose of introducing his own speculative opinion, And he says, "Those impressions are there"fore conveyed in diverging lines. Are they "likewise diffused equally in all directions? Such "is supposed to be the case with the rays of light

"proceeding from a luminous body. But al

"though analogy might induce us to extend "the principle, it cannot safely be admitted "without investigation."

If Dr. Speculative had been really ignorant of the fact, that the rays of heat do actually radiate in all directions from the centre of the heated body, like those of light, which every man of common understanding knows to be a truth; and which is one of the most unquestionable axioms in natural philosophy; Mr. Truth, if he had been permitted, would soon have conveyed this truth to his mind by the following simple Experiment.

By placing a canister, either round or square, all the sides of it being covered with black paint, in its proper situation upon the table at G, (see plate I.) in the centre of the circle E H IK; the reflector, and also the thermometer, being placed in their proper situations upon the board M; he could, by moving this board round upon its centre, have carried the reflector to any part of the circle he pleased; and by this means have shown Dr. Speculative, that the heat proceeding from the canister, produced the same effect upon the thermometer in every part of the circle. If it was possible to carry conviction to the mind of any Mr. Speculative, by

the testimony of his own senses, this simple Experiment must certainly have convinced him, that the rays of heat proceeding from the canister, did actually radiate from the centre of it like those of light; and, that they must, in consequence, be equally diffused through the adjoining space.

But as this simple appeal to our senses would have removed that doubt which Dr. Speculative had endeavoured to infuse into into our minds, and upon which he proposed to found his own speculative opinion, respecting the manner in which the rays of heat do issue from the heated body; and as it was necessary to conceal some part of the truth in those experiments which he now proposed to make, for the purpose of establishing his speculative opinion, which Mr. Truth would not consent to; we find that Dr. Speculative has taken the management of these experiments entirely upon himself. He according

ly proceeds with

He says

"Set the canister at a distance "from the reflector, not less than ten times its "own breadth, and dispose the apparatus as

"usual. In this position, the action of the whole

"of the blackened surface will be concentrated

The

66 upon the focal ball. Turn the side of the ca"nister more and more oblique, keeping its centre, however, always in the same place. "corresponding effects will gradually diminish; "at first gradually, and afterwards with accelerating activity."

As our honest friend Mr. Truth has not been permitted to open his mouth in this experiment it is proper to state what he would, and must have said, if he had been permitted to speak.In answer to Mr. Speculative's assertion, that, when the canister was placed at ten times its own breadth from the reflector, the action of the whole of the blackened surface will be concentrated upon the focal ball; he would have boldly replied, That is not true. And as a proof of it, he would have referred us to his first experiment; in which he showed us, that, when he brought the four sides of the canister coated with the different substances there mentioned, successively to front the reflector, they each of them produced a different effect upon the thermometer. He would have stated this as a proof that each of the four sides of the canister must necessarily occupy and exert its own particular power in a certain portion of the circle E H I K