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terous charge! How are “ obviously figurative expressions” tortured into a literal meaning! Which is the most rational supposition !--that the Eucratites, or Continentes, in the second century, viewed this passage through a false medium, and substituting the literal for the figurative expression (as the Romish interpreters have done, in Luke xxii. 19, 20. Matt. xxvi. 2623. Mark. xiv. 22-24, in favour of transubstantiation,) enforced on their followers what the passage in question was never designed to promote; or the other supposition, that the Eucratites -sprung up without any scriptural pretext, in a manner totally different froin all other heretical sects, and then forged a pretended Matthew to strengthen their newly fancied delusion ? But this is not all the complaint against Matthew ; for he relates that Christ gave the apostles a commission to baptize. Now Paul tells us, that in the commission of his apostleship, he was not a whit behind the very chiefest apostles: and yet he assures us, that he was not sent to baptize, but to preach the gospel! When will men possessed of a reasoning facully cease to obtrude upon the public such crudities, under the naine of criticisms ? What is plainer than that St. Paul did baptize some ; but would he baptize any without a commission? The fair inference then is, that he spoke in a comparative sense. His principal not his exclusive business was—to preach ; nor was this peculiar to Paul, for the commission in question is,“ Go teach all nations, baptizing them.” Who can question that instruction in Christian principles precedes, in point of real importance, the administration of a positive rite?"
This article is extended beyond the length we wished to assign it; but when the very foundation of the Christian faith, the authenticity of the received Scriptures, is openly attacked, we think it right to be rather particular in our observations, notwithstanding the folly of the assault. We have, however, one additional remark to offer, which is, that the principles of this publication will serve as a bold guide to universal scepticism and infidelity. Here it is maintained, that “the authority of the prophets alone is divine,” and even this linitation is still further limited to “ those whose predictions are in great part already fulfilled !” We understand that the author of these * Second Thoughts" is now numbered among the dead; but some of his disciples may see the expiration of sixty years. This is the term which he most confidently assigns, as the prophe tic period to the power of Antichristian Hierarchies. With him also it is a principle not to be controverted, that completed prophecy is the only criterion given us by God bimself, whereby we can ascertain the truth and divine authority of what is taught us as a revelation from him." And with respect to the Christian revelation, if the prophecies of the Apocalypse
have not been completed for above twelve centuries, we should be justified “ in rejecting the gospel itself, as not deserving our regard !” Prophecy, in the discussions of this writer, and his interpretation of prophecy,, seem to be only terms of the same import. Now, on his own principles, we should do right in rejecting Christianity itself, if the downfal of the apostate church were to be delayed above sixty years! He who could speak with such levity, sarcasm, disrespect, and licentious rudeness, not only of so respectable a character as the Bishop of Gloucester, but also of the commonly received sacred Scriptures, and especially the first book of the Christian canon, in opposition to the learning, piety, and impartial investigation of thousands, was well qualified to hazard the whole fabric of Christianity on such a quivering point. So much, patient reader, for these desul. tory and illiberal “ Second Thoughts;" we are sorry the ima partiality of criticism obliges us to say, that they deserve the additional epithets of impertinent, irrational, and visionary.
Art. III. An Experimental Inquiry into the Nature and Propagation
of Heat. By John Leslie. 8vo. pp. 562. Mawman, 1804. DELIGHTED with the apparently successful attempts of.
Dr. Wollaston, Dr. Herschel, and others, to determine the component parts of the solar light, we had indulged the hope, that some important discovery was at hand; and that, ere long, we should obtain a still more intimate knowledge of the nature and connection of light and heat. With this hope, we opened the volume before us; and considering the well-known abilities of the author, and the superior powers of his newly discovered instrument, the Cæsura, we doubted not of finding a near approach to the attainment of our wishes. The perusal of this work convinced us of the indefatigable industry, as well as the great mental powers, of its learned author : yet, we acknowledge, it has by no means gratified all our expectations. The theory here proposed, is founded on the supposition, that light and heat are different states of the same substance; and to establish it, a series of interesting experiments is described ; but the experiments of others, which seem to yield results cons tradictory to our author's theory, are not only denied their due influence, but treated with an air of superciliousness which cannot be excused.
Rejecting the opinion, that heat is simply a state or condition, of which all bodies are susceptible, and, of course, the notion of its dependence on internal vibrations, Mr. Leslie experiences no difficulty in admitting it to be a distinct and active principle. VOL. II.
By a close chain of reasoning, he is also enabled to conclude, that heat is an elastic fluid, extremely subtile and active. Thus far the opinions of Mr. Leslie accord with those of the generality of the philosophical part of mankind,' at the present day. But the next position which he lays down, varies so much from the present admitted doctrines of heat, as to demand a close examination. The position to which we refer is, that heat is only light in a state of combination. This conclusion, to establish which, most of the first part of our author's experiments and reasoning is employed, not only forms the basis, but constitutes almost the whole of the fabric which he has here erected. His next endeavour is very properly, therefore, to produce direct proofs of the identity of light and heat. * Light, he observeş, has two distinct states of existence, that of projection, and that of combination. The former is generally known and admitted : the latter state is inferred from the production of light from all substances, by collision, attrition, inflammation, the electric shock, &c. After some very ingenious remarks, by which it is expected that we should be enabled" to form some idea of the nature of those delicate and abstruse operations, which determine a particle of light to recoil, or to enter the substance of a body,” Mr. Leslie observes,
* But after, being urged by a general attraction, it has penetrated into the mass, its subsequent progress, through the ramified internal vacuities, is still liable to interruption. If it chance to pass too near a corpuscle, it will be powerfully solicited by a partial action, and turned aside from its course ; or if it encroach within a certain limit, its motion will be extinguished, and it will remain in a state of union. .Such appears to be the cause of the absorption of light.' pp. 157, 158.
But light thus absorbed into the substance of a body, is not supposed by Mr. Leslie entirely to lose its innate activity ; but to continue to exert, among its own particles, a strong mutual repul, sion. In confirmation of this, he remarks, that light must evi: dently be discharged froin luminous matter, by some effort of a repellent kind, which it would be contradictory to suppose, pro ceeded from the mass itself. To explain the divergency of the rays, he admits the necessity of a lateral repulsion, which may spread them in all directions ; aud concludes, that the particles of light must not only repel each other, whilst lodged within a body, but even after they have escaped, and are actually in mo tion. Extreme subtilty, powerful elasticity, or repulsion among its own particles, and eminent attraction to those of all other sub, stances are, he observes, characters which belong to the igneous fluid, and which also appear to belong to light while in a state of combination. This evidence of the identity of heat and light, though undoubtedly striking in every point, is properly admitted to be only presumptive. The proposition is, however, said to
bė supported by direct and unexceptionable proofs; and Mr. Leslie adds,
"I need mention only a single fact, which, duly weighed, will appear entirely conclusive. If a body be exposed to the sun's rays, it will, in every possible case, be found to indicate a measure of heat exactly proportioned to the quantity of light which it has absorbed. This statement is agreeable to common observation. A thin transparent substance, held in the sun-beams, scarcely acquires any sensible heat; and the imprese sion of the solar rays on the bright polished surface of a metallic body is equally feeble. A mercurial thermometer, and one whose bulb is filled with deep tinged alcohol, are very differently affected in the sun. The heat which dark-coloured substances conceive from the afflux of light, is well known. But, on closer' examination, the principle above stated will appear to apply with perfect accuracy. The most delicate trials evince, that, in like circumstances, the elevation of temperature always corresponds with the greatest nicety to the degree of absorption. pp. 160, 161.
After adducing several other observations, Mr. Leslie concludes by saying, “ it were easy to multiply arguments and illustrations. But enough has, I presume, been stated to establish the conclusion, that heat is only light in the state of combination."
We have here placed before our readers, in as connected a manner as we are able, the ground-work of the theory which this yolume is intended to support ; and, in doing this, we have as much as possible endeavoured to adhere to the words of its author. We shall now proceed to consider and determine the weight of the objections to which this theory appears liable; and which are said, by the author, not to be formidable, but to admit of satisfactory answers.
The first of these is founded on the revival of certain metallic oxyds, which has been supposed to be produced by the operation of light alone. This property, Mr. Leslie asserts, does not, however, in strictness, exclusively belong to light; the simple application of heat is capable, he says, more or less, of producing analagous effects. Reasoning from the almost inconceivable rapidity, with which the particles of light are impelled, and from the vehement, though diffuse re-action produced in the obstacle by which their progress is stopped, he supposes, that the peculiar energy of light may be ascribed to its force of impulsion : and because the slight blow of a hammer will revive silver and mercury with violent explosion, he asks, why should not the stroke of light, in its gradual accession, silently operate, in some degree, a similar effect on the nitrate of silver. That opinion must greatly need support, which would claim it from such loose reasoning and vague conjecture. Between the fact wbich has been adduced, and the circumstance which is assumed, N %
no analogy appears to exist. In the former it readily occurs to the mind, that the particles of the substance are suddenly brought by percussion within the sphere of each others attraction; and new combinations take place in consequence of the different chemical attractions which are thus enabled to act. But in what manner is it conceivable, that the stroke of light can, by the force of its impulsion, produce a similar effect? Why oppose a conjecture so feebly founded, to the more plain and obvious explanation derived entirely from the powers of chemical affinities, by which we are taught, that while the deoxydizing substance is abs.rbing the light, it yields up the oxygen for which its attraction is diminished. Mechanical impulse is unnecessary in explanation of these phenomena: its introduction, therefore, is reprehensible. True philosophy, the learned writer of this work well knows, admits no superfluous agents.
That the simple application of heat is capable of causing some effects, which are analagous to those produced by light, as in the de oxydizement of metallic oxyds, is not denied. This, however, does not prove much in favour of the identity of heat and light; since similar effects are produced by other substances, which partake, in no other respect, of the characters of either heat or light.
The influence of light on the colour of vegetables appears to be an objection of still greater weight. No analagous effect of heat has presented itself to the author, whose attempts to invalidate the objection are without force. Instead of considering the blanching of plants which grow in the dark, as an effect immediately and almost peculiarly dependent on the absence of light, which it undoubtedly is, Mr. Leslie supposes, that it proceeds merely froin the unhealthiness of the plant : and that the influence of darkness extends no farther than to produce a morbid state.
* The appulse of the rays of light must invigorate all the functions of vegetable life. Light seems requisite to the health of plants. Deprived of its beneficial energy they become flaccid and pale, and sickly. Their whiteness is only a symptom of disease.' p. 164.
These positions are not to be implicitly admitted ; a distinction is here absolutely necessary. The whiteness of the plant is undoubtedly a disease peculiarly dependent on the absence of light: it is not a symptom of a general morbid affection of the plant. Plants may suffer this change and still grow with a considerable degree of luxuriancy. Instances of this kind are mentioned in Dr. Black's lectures, by Professor Robison, and similar instances may be daily observed in the blanched plants of celery and endive, and to a very great degree in the shoots from potatoes kept a year or two in a dark and