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expel a quantity of heat, and raise the temperature above the true mean. It is not improbable that the true mean temperature between 32° and 212, may be as low as 110° of Fahrenheit.

"It has been generally admitted, that if two portions of any liquid, of equal weight, but of different temperatures, be mixed together, the mixture muft indicate the true mean temperature; and that inftrument which correfponds with it, is an accurate meafure of temperature. But if the preceding obfervations be correct, it may be queitioned whether any two liquids will agree in giving the fame mean temperature upon being mixed as above.

"In the prefent imperfect mode of eftimating temperature, the equable expanfion of mercury is adopted as a fcale for its measure. This cannot be correct, for two reafons, 1ft, the mixture of water of different temperatures is always below the mean by the mercurial thermometer; for inftance, water at 320 and at 212° being mixed, gives 119° by the thermometer; whereas it appears from the preceding remarks, that the temperature of fuch mixture ought to be found above the mean 122°; 2dly, mercury appears by the most recent experiments, to expand by the fame law as water; namely, as the fquare of the temperature from the point of greateft denfity.-The apparent equal expanfion of mercury arifes from our taking a fmall portion of the fcale of expanfion, and that at fome diftance from the freezing point of the liquid." And in the next page this author fays, "Some time ago it occurred to me as probable, that water and mercury, notwithstand. ing their apparent diverfity, actually expand by the fame law, and the quantity of expanfion is as the fquare of the temperature from their respective freezing points. Water very nearly accords with this law according to the prefent fcale of temperature, and the little deviation obfervable is exactly of the fort that ought to exift, from the known error of the equal divifion of the mer curial fcale. By profecuting this enquiry, I found that the mer. curial and water fcales divided according to the principle juft mentioned, would perfectly accord, as far as they were compas rable: and that the law will probably extend to all other pure liquids; but not to heterogeneous compounds, as liquid folutions of falts."

After several other remarks, Mr. D. ftates the following remarkable analogies:

"1. All pure homogeneous liquids, as water and mercury, expand from the point of their congelation, or greatest density, a quantity always as the fquare of the temperature from that point.

"2. The force of fteam from pure liquids, as water, ether, &c. conftitutes a geometrical progreffion to increments of tempe rature in arithmetical progreffion.

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"3. The

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3. The expanfion of permanent elaftic fluids is in geometrical progreffion to equal increments of temperature.

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4. The refrigeration of bodies is in geometrical progreffion in equal increments of time.

"A mercurial thermometer graduated according to this prin ciple will differ from the ordinary one with equidifferential fcale, by having its lower degrees fmaller and the upper ones larger; the mean between freezing and boiling water, or 122° on the new fcale, will be found about 110° on the old one.

Mr. D. then adds a table exhibiting the numerical calcula tions illuftrative of the above-mentioned principles.

In the fecond fection, which treats principally of the expanfions of liquids and folids by heat, a variety of facts, experiments, and appropriate remarks are contained, to which we would particularly direct the attention of the philofophical reader; but it is not in our power to give a clear, and, at the fame time, fuccinct account of the numerous particulars. We fhall only extract the refults of the experiments and calculations relative to the expanfions of liquids.

The greatest denfity of water, as this author thinks, is not at 40°, according to other philosophers, but at or near the 36th degree of the old thermometer, or between 37° and 38° of that which he has propofed.

The real expansion of mercury from 82° to 212, he states

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Alcohol expands about of its bulk for 180°, from -8°

to 172°.

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Oil, and linfeed oil, expand about 8 per cent. by 180° of temperature.

Oil of turpentine expands about 7 per cent. for 180°. Sulphuric acid, of the fpecific gravity 1,85, expands about 6 per cent. from 32° to 242°.

Nitric acid, of the specific gravity 1,40, expands about 11 per cent. from 32° to 212°.

Muriatic acid, of the fpecific gravity 1,137, expands about as much as the fulphuric acid.

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Sulphuric ether," this author fays, "expands after the rate of 7 per cent. for 180° of temperature. I have only compared the expanfion of this liquid with that of mercury from 60° to go In this interval it accords fo nearly with mercury, that I could perceive no fenfible difference in their rates. It is faid to freeze at 46°."

Refpecting the expanfions of folids, Mr. Dalton contents himfelf with ftating the refults of the experiments of Smea

ton,

ton, Ellicot, and Borda; and laftly he adds a table exhibiting fome of the most remarkable effects which are produced at certain temperatures; fuch as the fufion of metals, the boiling of certain liquids, &c.

In the fifth fection, which treats of the quantity of heat evolved by combuftion, this author, amongst other important particulars, defcribes a curious fimple apparatus for determining the quantity of heat extricated by the combuftion of inflammable elaftic fluids; but for the defcription of this apparatus, and likewife for the refults of the experiments. that were made with it, we must refer our readers to the work itself. In the fequél of the same section, the refults of other experiments on the fame fubject are contained, together with fuitable remarks.

The natural zero of temperature, or of the total privation of heat, forms the fubject of the fixth fection, wherein this author gives the hiftory of the various methods by which the determination of that point has been attempted. To each of those methods he adds his remarks, and the refult of his experience. The mean of all those results shows that the zero of temperature is about 6000 below the temperature of freezing water; and this, he fays, we are authorized to admit until fomething more decifive is made to appear.

The feventh fection contains an epitome of the refults of Profeffor Leflie's important experiments on radiant heat, after which Mr. Dalton ftates feveral experiments which gave him reason to diffent, in a certain degree, from fome of Profeffor Lellie's conclufions.

The eighth fection contains a particular examination of a well known fact refpecting the atmosphere; namely, that the atmosphere, in all places and feafons, is found to decrease in temperature according as we afcend, and nearly in an arithmetical progreffion. The question which Mr. Dalton endeavours to answer is, whence does this diminution of temperature arife?

For this purpose, he, in the first place, ftates the common folution, which is, that the rays of the fun paffing through the atmosphere to the earth, heat the latter, and trom the latter the heat is then communicated to the contiguous part of the atmosphere, whilft the fuperior ftrata receive less heat in proportion as they are more remote from the furface of the earth. On examination, however, he finds that the latter part of this explanation is inadmiffible; for it is well known that heated air afcends with great rapidity; in confequence of which it fhould feein, that at greater diftances from the furface of the earth, the temperature ought to be

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higher

higher and higher, contrary to obfervation. This, and other remarks, gradually induced him to reft the explanation upon the bafe of a new principle, which feems to be pretty fairly established by his fubfequent reafoning and illuftration. The principle is,

That the natural equilibrium of heat in an atmosphere, is when each atom of air in the fame perpendicular column is poffeffed of the fame quantity of heat; and confequently, the natural equilibrium of heat in an atmosphere is when the temperature gradually diminishes in afcending."

In the laft fection of the first chapter, Mr. D, attempts to explain the phenomena attendant on the congelation of water. He firft ftates the phenomena, and then adds the principle upon which he grounds his explanation; but it is not in our power to give a concife and fatisfactory idea of this expla nation, efpecially for want of the figures to which he refers, and which are delineated in one of the plates which accompany the work.

The fecond chapter treats of the conftitution of bodies, and is divided into four fections; but the fecond of those fections is by far the longest and the most elaborate of them all. Its title is, On the conftitution of mixed elastic fluids.

The phenomenon which this author endeavours to exa, mine and to explain, was, as it feems, first noticed by Dr, Priefley, and it has, after Priestley, excited the wonder and the induftry of many fucceeding philofophers, particularly of the author of the prefent work. The phenomenon is, that when elaftic fluids of different fpecific gravities (but whofe particles do not unite chemically upon mixture) are placed together in one veffel, they become uniformly diffafed through each other without the leaft regard to their different gravities; whereas this is by no means the cafe with liquids.

In explanation of this phenomenon, Mr. D. proposed an ingenious theory, which was announced to the world through various channels; but it met with confiderable oppofition, and feveral able writers publifhed their remarks upon it. Of those writers the principal are, Mr. Berthollet, Dr. Thomfon, Mr. Murray, Dr. Henry, and Mr. Gough. Now in the prefent publication, Mr. D, firft ftates his hypothefis, in the next place he confiders the objections which have been made to it by the above-mentioned authors, and lastly endeavours to modify his theory agreeably to the fuggeftions of his further experiments and more mature reflection. Mr. Dalton's hypothelis, in fhort, is,

That

That the particles of one gas are not elaftic or repulfive in regard to the particles of another gas, but only to the particles of their own kind. Confequently, when a veffel contains a mixture of two fuch elaftic fluids, each acts independently upon the veffel, with its proper clafticity, juft as if the other were abfent, whilft no mutual action between the fluids themselves is obferved."

Mr. D. anfwers the objections which have been made to this hypothefis with propriety and acutenefs; cafting, at the fame time, confiderable light on the whole fubject of elaftic and atmospheric fluids.

The third chapter of this work is a very fhort one, for it occupies only five pages. It contains fome general and hypothetical ideas, principally relating to the primary particles of bodies, both fimple and compound. Thofe ideas are illuftrated by references to figures which are annexed.

Upon the whole this work contains four copper-plate engravings, with proper explanations of the figures, &c.

After a careful perufal of Mr. Dalton's prefent work, it must be acknowledged that his inveftigations, experiments, and obfervations, are generally directed towards the hypothetical and the fpeculative. The bufy world is juftly inclined to prefer what is practically useful, to the abftrufe inveftigations of theory or hypothefis; yet it muft be obferved, that in natural philofophy the practical part of a fubject is much promoted, and often directed into a regular channel, by the eflablishment of a rational, or even plaufible, theory; nor can fuch a theory be formed without a ftrict examination of facts, and the unreftrained difcullion of hypothefis.

The well known facts relative to the fubjects of this work have been compiled, condensed, and expreffed by Mr. Dalton in a clear and correct manner. To thofe he has added the accounts of other new facts. His hypothefes are free from any apparent abfurdity; and his anfwers to his various opponents are, expreffed with moderation and propriety. We, therefore, hesitate not to recommend the careful perufal of this inftructive work to the philofophical world,

ART. V. The Travels of Capts. Lewis and Clarke, from St. Louis, by Way of the Mijouri and Columbia Rivers, to the Pacific Ocean; performed in the Years 1801, 1805, and 1806, by Order of the Government of the United States. Containing Delineations of the Manners, Cuftoms, Religion, &c. of the Indians, compiled from various authentic Sources, and original

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