After giving fo 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 result 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) "balf 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 90, added to the number expreffing the temperature of the colder liquor, (32) or fubftracted from the number expreffing that of the botter (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 eflay, from M. De Luc; but there the temperature of the fame mixture is made to be 180, which is faid to be the arithmeti cal mean between 32 and 212.

[B] It is not merely to prevent ambiguity," that Mr. Crawford makes a diftinction between the abfolute and sensible heat of a body for that distinction forms the very bafts 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 thermometers 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 observing 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 propofed 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, thould have concurred in the opinion, which feveral of the latter, in particular, alcribe to Dr. Priestley; "that atmofpherical air is changed, in refpiration and other proceffes, into fixed air: especially as Dr. Priestley has more than once, we believe taken notice of this mifapprehenfion of his meaning. This mitake, in a certain degree, affects fome of the Author's conclufions drawn from his experiments made on fixed air; on a fuppontion

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 phlogisticated air; and parti cularly with the air that is phlogifticated by animal refpiration."

[D] The Author's theory relating to animal heat may perhaps be most compendiously and beft explained as follows, in addition to the extracts given by our Correfpondent. From the experiments made to afcertain the abfolute heat refiding in bodies, Mr. Crawford infers that a large quantity of fire is contained in atmospherical air, as a conflituent principle; that living animals acquire their heat from this ftock contained in the air, by means of the phlogiston 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 procefs is fuppofed to go on, fimilar to a chemical eledive 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 phlogifon will leave the blood to combine with the air; because the attraction of the air to the phlogiston 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 deposit 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 phlogifton, by the process of refpiration, afterwards acquires fresh phlo. gifton 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 diffufe it over the whole fyftem. Thus, in the lungs, the blood is continually difcharging phlogifton into the air, and abforbing 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 phlogifton to the blood; the remainder becomes redundant, or is converted into moving and fenfible heat, or that heat which is the object of our senses.

With respect to fome of the Author's experiments, we think it expedient to offer an observation which has not been made by our Correfpondent. 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 animal life.

Though the Author fhews a minute attention to every circumflance that can be supposed to influence the refults in his experi. ments;-particularly to the temperature of the veffel in which the mixtures are made; the time spent in mixing the fubftances 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.

fo

fo very small, that doubts will probably be entertained whether they will justify his deductions from them.

It will be doubted, for instance, whether any decifive conclufion may be drawn from obferving the temperatures of a mixture of two fluids, differing in specific gravity fo very confiderably as water, and common, or dephlogifticated, air; though he gives to the latter 100 degrees of heat more than to the former. Thus a pint of atmospherical air, contained in a bladder, and raised to the tempera ture of 163 degrees, is immerfed in a pint of water at 63 degrees; that is, in a quantity of fluid containing above 800 times more mat ter than itself. Had the atmospherical air contained the fame abfolute heat with water, the Author calculates that it would have com. municated to the water nearly the one-fixteenth part of a degree of heat but it communicated to it one intire degree of heat.'-He concludes therefore, that afmofpherical air muft contain at least 16 times as much abfolute heat as water. From fimilar experiments made with dephlogisticated air, he calculates that it communicated three degrees of heat, &c.

Even the greatest of these differences is fo fmall, that there is reafon to fufpect, notwithstanding all the Author's accuracy and care, that they may poffibly have proceeded from caufes different from thofe here affigned. With refpect to fuch differences, there is fome reafon to apprehend that they may proceed either from caufes wholly unknown and unfufpected; or from others, the effects of which are too difficult, or minute, to be accurately afcertained.

Notwithstanding this remark, which cannot well have escaped the fagacity of the Author himfelf; we hope he will profecute his ingenious inquiries, for which he appears to be fo well qualified. There are undoubtedly many phenomena in nature, well explained by this hypothefis; which, as well as the Author's various and well imagined experiments, deferve the attentive confideration of philofophers.

ART. XIV. A Flan of the navigable Canals made, and now making, in England. Lowndes.

HIS Plan (as we learn, by a new edition of The History

Tof Inland Navigations, publifhed with it) is done from

actual furveys, made and drawn by Mr. Hugh Henshall, engineer, and fucceffor to Mr. Brindley; it cannot, therefore, fail of proving very acceptable to the public. It gives a clear and diftinct view of one of the most extenfive and important general improvements that this nation ever experienced; the confe quences of which must be as durable as the exiftence of these valuable works. When a manufacturing and commercial nation, through excefs of riches, luxury, and taxation, can no longer bring its productions to market at a moderate price; and when other countries, by reafon of cheapnefs, begin to underfell it, the decay of fuch rich nation would then be infallible, and extremely rapid, if this natural caufe of declenfion were not retarded by the exertions of genius, in the ap

plication

plication of mechanical powers to the business of manufactures; -by which means alone the destructive effects of abundant riches, and high taxes, can be fufpended, and an industrious nation, in fuch circumftances, be preferved from ruin. The manufactures of Birmingham, Manchester, Sheffield, &c. have long exifted upon these principles; and the manufacturers have been enabled, by the ingenuity and variety of their mechanical inventions, to fupport a rival trade against all Europe, and fupply countries (where human labour is much cheaper than in this) with their commodities.

But among all these improvements, there are none fo fundamental, fo extensive, and fo powerful, as that amazing system of water roads, exhibited in the plan now before us; and which realife all the advantages to this nation, long fince foretold in various publications on this fubject. All the central parts of the kingdom, and almost all the manufactures, now enjoy, or foon will enjoy, the unfpeakable advantage of a reduction of more than two-thirds of the price of carrying all heavy articles; many thousands of devouring horses will be rendered unneceffary;-and if our public measures were conducted with as much wifdom and fpirit as the affairs of individuals, and those who take upon them to protect and lead us, would please either to act their part well, or do nothing, there is no doubt but this nation might ftill go on improving; and that its natural and artificial advantages might fupport it in wealth, honour, and power, for many ages.

But before we take leave of the Plan under confideration, we cannot help obferving one capital defect in the execution of this great fyftem of canals, which, we are well informed,. might eafily have been prevented when the act for the Staffordfhire navigation, or the Great Trunk, as Mr. Brindley called it, was obtained. The Duke of Bridgewater's canal, the Staffordfhire canal, and confequently, all thofe that now do, or ever may fall into them, by a narrow and selfish policy, are made to terminate in the Tide-way of the river Merfey; when they ought to have been carried over that river by a grand aqueduct into Lancashire, and to the port of Liverpool; where they might have been joined by other canals and branches from different parts of Lancashire and Yorkshire; and the whole fyftem of canals might reciprocally have communicated with each other, without going into a tide's way, or making it neceffary to trans-fhip the goods--This noble plan was propofed at the time, by a zealous and active friend to these undertakings; a meeting was had upon it at Runcorn, the place where the navigation should have croffed the river; all the parties declared, it would be the best plan for the public intereft; Mr. Brindley approved of it, and declared it to be practicable, both

Cc 2

at

at this meeting and before the Houfe of Commons ;-where he was very particularly examined upon this point ;-and yet other views and interefts prevailed, and this great work was left to be completed by pofterity, for whofe fake we leave this memorandum of a tranfaction in which they may be interested; at the fame time, referring them for farther particulars to the Journals of the Houfe of Commons.

There is another obvious defect in this fyftem of canals, for want of an extenfion of the Staffordshire canal from fome part near Derby to Chesterfield, which certainly will be removed when the proprietors of the Staffordfhire and Chefterfield canals, and the land-owners between Derby and Chefterfield come to understand their true interefts; and to confider the benefit that muft arife to them and the public from the propofed communication; by which means, the goods from Staffordshire and the neighbouring counties, would be delivered above fifty miles lower upon the Trent than at prefent, and the county of Derby receive great advantages in the conveyance of its natural productions, and in many new manufactures and eftablishments, which thefe improvements never fail to produce.

This new edition of the History of Inland Navigations contains feveral ufeful tables of diftances, rates of freight, &c.and is, on the whole, a valuable collection of papers relative to the canals that have been projected, and executed, in this country. The laft letter in this compilation takes notice of another great mechanical improvement, for which this nation is indebted to the philofophic fpirit of the age, and to the abilities of thofe ingenious philofophers and artists Meffrs. Watt and Boulton, whofe skill and activity we hope will be amply rewarded by their country The writer, after fpeaking of the lime-kilns, near the Bridgewater Navigation, adds- Nor can I pafs filently over the capital and new erected Salt-works, built upon the banks of the navigable canal at Thurlwood, in Chefhire, the property of Meflrs. Salmon and Purlington. In an adjoining valley, they have fixed a fire-engine, conftructed by Mell. Watt and Boulton, which in the wafte of three hundred weight of coals (value nine-pence) does in twelve hours throw up, to the height of a hundred yards, not lefs than twenty-four thoufand gallons of brine; which is received in a very large refervoir, and from thence conveyed to the falt-pans, where the falt is extracted and loaded into barges, in which it is carried into Staffordshire, Derbyshire, and the neighbouring counties.'

We have caft up the lengths of the feveral canals included in the plan, and we find, that they amount to 556 miles, and

See an account of Mr. Watt's great improvements on the invention of the Steam Engine, Rev. vol. Ivi. p. 40.

4

a few