no doubt, in part at leaft, by answering the cravings of nature to the full whereas they should be denied a full gratification, as little fuftenance for that fpace of time would anfwer much better. If any think this hint, by way of caution, impertinent, there is reason to doubt that they are yet too much strangers to the nature of true worship, and the many impediments in the way of its performance: that abovementioned being none of the leaft. I was quite hut up as to miniftry in the afternoon.' Mr. Griffith hath not informed us whether he was shut up through a full belly that overpowered the fpirit, and kept it down under a grofs load of flesh; or that fympathetic principle, which he frequently fpeaks of, that anfwers to the fituation of others, and feels, by a fecret impulfe, the workings of a good or an evil spirit in the fociety of Friends. This is the very quinteffence of myfticifm: and foars above the comprehenfion of all but Quakers indeed. This spiritual fympathy-this interchange or reciprocal communication of fecret feelings, is particularly defcribed by the celebrated Robert Barclay in his Apology and as it enters deeply into the ancient fyftem of Quakerifm, we think it fufficiently curious to be laid before our Readers: "Such is the evident certainty of that divine ftrength that is communicated by thus meeting together, and waiting in filence upon God, that fometimes when one hath come in, that hath been unwatchful and wandering in his mind, or suddenly out of the hurry of outward bufinefs, and fo not inwardly gathered with the reft: fo foon as he retires himself inwardly, this power being in a good measure raised in the whole meeting, will fuddenly lay hold of his fpirit, and wonderfully help to raise up the good in him, and beget him into the fenfe of the fame power, to the melting and warming of his heart; even as the warmth would take hold upon a man that is cold coming into a five; or as a flame will lay hold upon fome little combuftible matter being near unto it. Yea, if it fall out, that feveral met together be ftraying in their minds, though outwardly filent, and fo wandering from the measure of grace in themselves (which through the working of the enemy, and the negligence of fome, may fall out), if either one come in, or may be in, who is watchful, and in whom the life is raised in a great measure; as that one keeps his place, he will feel a fecret travail for the reft in a Sympathy with the feed, which is oppreffed in the other, and kept from arifing by their thoughts and wanderings. And as fuch a faithful one waits in the light, and keeps in the divine work, God oftentimes anfwers the fecret travails and breathings of his own feed through fuch a one; fo that the rest will find themfelves fecretly fmitten without words; and that one will be Bb 4 as From Dr. Priestley's experiments, it alfo appears, that arterial blood has a strong attraction to phlogifton. During the circulation, therefore, the blood which had been dephlogifticated by the process of respiration, will imbibe the phlogiston from thofe parts which retain it with the leaft force, that is, from the putrefcent parts of the fyftem. Accordingly, the venous blood, when it returns to the lungs, is found to be highly impregnated with phlogifton. In proportion as the blood becomes again combined with phlogifton in the courfe of the circulation, it will gradually give out that heat which it had received in the lungs, and diffuse it over the whole system. Mr. Crawford endeavours to confirm this theory, by experiments made in order to determine the absolute heat of the blood which paffes from the lungs to the heart, by the pulmonary vein, and of that which paffes from the heart to the lungs, by the pulmonary artery. In the fourth fection, a very ingenious application is made of these principles, to explain the moft remarkable facts relating to animal heat [D]. Before we leave this part of our Author's fubject, it may not be improper to remark the difference between his theory, and that which has been lately published by Dr. Leflie*. According to Dr. Leflie, animal heat is produced by the evolution of the phlogifton of the blood in the courfe of the circulation; according to Mr. Crawford, it is produced by the heat which the blood depofits in confequence of its being gradually impregnated with phlogifton. The former feems to conceive heat and phlogifton as connected together; the latter confiders them as acting in fome measure in oppofition to each other. With refpect to Dr. Leflie's hypothefis, it may be observed, that it is altogether inconfiftent with thofe experiments of Dr. Prieftley's, from which it appears, that arterial blood has fo ftrong an attraction to phlogifton, that it is capable of feparating it from fixed and phlogifticated air. If this be the fact, how fhall we account for the evolution of the phlogiston of the blood, during the time of circulation? Our Author's theory with refpect to the inflammation of combuftible bodies, is founded on the fame principles as his doctrine concerning the heat of animals. According to him, the heat which is produced by combuftion is derived from the air, and not from the inflammable body. In fupport of this doctrine, he reafons thus: Inflammable bodies abound with phlogifton, and contain little abfolute heat; atmospherical air, on the contrary, abounds with abfolute heat, and contains little phlogifton. In the procefs of inflammation, the phlogifton is separated from the inflammable body, and combined with the * See Review for May laft, p. 385. air; the air is converted into fixed and phlogisticated air, and at the fame time gives off a very great proportion of its abfolute heat, which, when extricated fuddenly, burfts forth into flame, and produces an intenfe degree of fenfible heat. We have found by calculation, that the heat which is produced by the converfion of atmospherical into fixed air is fuch, if it were not diffipated, as would be fufficient to raise the air fo changed to more than twelve times the heat of red hot iron. It appears, therefore, that in the process of inflammation, a very great quantity of heat is derived from the air. It is manifeft, on the contrary, that no part of the heat can be derived from the combustible body; for the combustible body, during the inflammation, being deprived of its phlogifton, undergoes a change fimilar to that which is produced in the blood by the procefs of refpiration; in confequence of which, its capacity for containing heat is increafed. It therefore will not give off any part of its abfolute heat, but, like the blood in its paffage through the lungs, it will abforb heat. The calx of iron, for example, is found to contain more than twice as much abfolute heat as the iron in its metallic form; from which it follows, that in the procefs of inflammation, the former muft neceffarily abforb a quantity of heat, equal to the excess of its heat above that of the latter. Now, from whence does it receive this heat? It cannot receive it from the iron. For the quantity of heat in the calx is more than double of that which was contained in the iron, previous to the calcination. But in the burning of iron, the phlogifton is feparated from the metal, and combined with the air; and it has been proved, that by the combination of phlogifton with air, a very intenfe heat is produced. From hence it is manifeft, that in the inflammation of iron the atmospherical air is decompofed, a very great proportion of its abfolute heat is feparated, part of which is abforbed by the calx, and the reft appears in the form of flame, or becomes moving and fenfible heat. We may conclude, therefore, that the fenfible heat, which is excited in combuftion, depends upon the feparation of abfolute heat from the air, by the action of phlogifton.' In this manner, our Author attempts to explain the principal phenomena of animal heat, and of the inflammation of combuftible bodies, from the general fact, that the capacities of bodies for containing heat are diminished by the addition of phlogiston, and encreafed by its feparation. Towards the conclufion of the Treatife, he applies the fame principle to account for a variety of natural phenomena. From the obfervations made in this part of his work, it appears, that many important effects are produced in the univerfe, in confequence of the mutual oppofition of phlogifton and fire. After After giving so full an account of the principal doctrines contained in this performance, it is unneceffary for us to recommend it to the attention of our readers. The Author, whatever may be the fate of his theory, is evidently poffeffed of uncommon ingenuity; and if he be, as we are affured he is, a very young man, the public may form high expectations from his future labours. [A] How right foever the refult of the example, here given by the Author, may be, in making 122 the temperature of the two equal portions of water mixed together, at the respective temperatures of 32 and 212; it does not appear to us to agree with the rule which immediately precedes it, and which the Author quotes from Boerhaave; nor with the refult of the fame example given likewife by Boerhaave. The number 122 does not exprefs (as the rule requires) half the excess of the hotter above the colder fluid," which is only 90 degrees, and is the number affigned by Boerhaave*: but it is half the excefs, or go, added to the number expreffing the temperature of the colder liquor, (32) or fubftracted from the number expreffing that of the hotter (212) = 122: or, in other words, it is the arithmetical mean, or half the fum, of the two numbers.-It appears remarkable to us, that the very fame example is repeated at the end of this effay, from M. De Luc; but there the temperature of the fame mixture is made to be 180, which is faid to be the arithmetical mean between 32 and 212. : [B] It is not merely to prevent ambiguity," that Mr. Crawford makes a diftinction between the absolute and fenfible heat of a body for that diftinction forms the very bafis of his whole theory. In order to understand his experiments, and his deductions from them, it is abfolutely neceffary to attend to the effential diftinction, which the experiments, already recited by our Correfpondent, prove to exist between the fenfible and the abfolute heat of bodies. The first of thefe is directly indicated by the thermometer: whereas the abfolute heat of a body becomes known to us only by inference and calculation; or by mixing together heterogeneous bodies, which have no known chemical action on each other, and obferving the changes produced in the fenfible heat of the different mixtures, as fhewn by the thermometer. By obferving the difference between thefe refults, and thofe that occur when portions of the fame fluid, of different temperatures, are mixed together, it is proposed to detect the abfolute heat of bodies, or their different capacities for containing heat. [C] It is rather fingular that our ingenious Author, as well as fome foreign philofophers, fhould have concurred in the opinion, which feveral of the latter, in particular, afcribe to Dr. Priestley; that atmospherical air is changed, in respiration and other proceffes, into fixed air: efpecially as Dr. Priestley has more than once, we believe, taken notice of this mifapprehenfion of his meaning. This mistake, in a certain degree, affects fome of the Author's conclufions drawn from his experiments made on fixed air; on a fuppofition Boerhaave's Chemistry, tranflated by Shaw, vol. i. pag, 290. that that the atmospherical air expired from the lungs had been converted into fixed air. Air injured by refpiration is principally phlogifticated air, and not fixed air; though it certainly exhibits figns of its containing a portion of the latter principle. The Author therefore fhould have made his experiments with phlogifticated air; and parti cularly with the air that is phlogisticated by animal refpiration. [D] The Author's theory relating to animal heat may perhaps be moft compendiously and beft explained as follows, in addition to the extracts given by our Correfpondent. From the experiments madeto afcertain the abfolute heat refiding in bodies, Mr. Crawford infers that a large quantity of fire is contained in atmospherical air, as a constituent principle; that living animals acquire their heat from this stock contained in the air, by means of the phlogifton contained in the blood; which combining with the air, caufes the latter to part with a portion of its abfolute heat, or latent fire. In short, a process is fuppofed to go on, fimilar to a chemical elective attraction. The air, in refpiration, is received into the lungs, containing a great quantity of abfolute heat. The blood is returned from the extremities, highly impregnated with phlogifton; and by this impregnation its capacity for containing heat is diminished. The phlogifton will leave the blood to combine with the air; because the attraction of the air to the phlogifton is greater than the attraction of the blood to that principle. On the combination of the phlogiston with the air, the latter is obliged to depofit a part of its abfolute heat; which immediately unites with the blood; the capacity of which to receive it is at the fame time increased by the feparation of its phlogifton. The blood thus dephlogifticated, or deprived of a part of its phlo. gifton, by the process of refpiration, afterwards acquires fresh phlogifton in the courfe of the circulation; and as its capacity for containing heat is diminished by this combination, it will gradually part with the heat which it had received in the lungs, and diffuse it over the whole fyftem.-Thus, in the lungs, the blood is continually discharging phlogifton into the air, and absorbing heat from it in return and in the courfe of its circulation through the body, it is continually imbibing phlogiston from the fyftem, and emitting heat into it. This heat being more than can be abforbed by thofe parts of the fyftem which communicate the phlogiston to the blood; the remainder becomes redundant, or is converted into moving and senfible heat, or that heat which is the object of our fenfes. With respect to fome of the Author's experiments, we think it expedient to offer an observation which has not been made by our Cor refpondent. We allude to thofe, particularly, from which the Author infers that the quantity of abfolute heat contained in air is very nearly in proportion to its purity, or to its power in fupporting ani mal life. Though the Author fhews a minute attention to every circumflance that can be fuppofed to influence the refults in his experiments;-particularly to the temperature of the veffel in which the mixtures are made; the time spent in mixing the substances together; the degree of agitation; the temperature of the atmosphere at the time, &c.-yet, in fome of them, it must be confeffed, the feale is REV. Nov. 1779、 Сс fo |