fenfibly, that is, pafs eafily from one body to another, is capable of producing, or, more properly, of preferving fluidity? that the latent heat never disappears, or lofes its influence in preferving fluidity, till the cold has become so far fuperior as to bring the fluid to the freezing point? that then it disappears gradually and but gradually, elfe the fluid would be converted at once into ice; which is not the cafe, greater acceffions of cold, and of a longer duration, being requifite to make fluids affume a folid form.

In the fame manner, the abforption of latent heat is obfervable in the reduction of a folid to a fluid-as of ice to water a very great quantity of heat is abforbed before the ice begins to melt, a quantity more than fufficient to bring thetemperature above the freezing point, if the heat fo abforbed acted fenfibly, or could be measured by a thermometer. What then becomes of this large portion of heat, which has inconteftably entered the ice? It has been abforbed by the ice, and lies concealed in it in a latent form.

In this way are we to account for the large quantities of ice to be seen on the furface of the earth after long frofts, for fome days after the thaw has commenced. After fevere frofts, the weather is generally very warm: how comes it that the ice exposed to the heat of the air is not immediately melted? Each piece of ice being examined by the thermometer, will be found to be cooled to the freezing point; yet it cannot be denied, that every such piece muft be affected by the warmth of the atmosphere, and the influence of the fun. What then becomes of this heat, which, as far as we can judge, has no fenfible effect? It is evidently abforbed by the ice, and contained in it latent. In the fame manner, ice, in ice-houfes, notwithstanding all the precautions that are used, could not fail of melting, if all the heat it received acted fenfibly; but that is not the cafe, great part of it being abforbed, remains latent, and, of course, has no fenfible effect.

The following experiment is decifive upon this fubject. Into a veffel was put fome water cooled nearly to the freezing point; into another a quantity of ice: by a thermometer the change made upon the water during the first halfhour, by the temperature of the warm room, in which the veffels were fufpended, was observed, and it was found to have raifed the liquor 7 or 8 degrees above the freezing point: no change was obfervable in the ice, fave that a very little of it was melted; but what was fo melted, was found, by the thermometer, to be equally cold with the mafs of ice. The veffels hung in this manner for 11 1-half hours, at the end of which time all the ice was melted. Now, as each veffel received from the temperature of the room in which it was placed, about 7

degrees

degrees of heat every half hour, it is evident, the vessel containing the ice, muft, at the end of 11 hours and a half, have received upwards of 140 degrees of heat; that is, the quantity of heat flowing into the veffel, during that time, must have amounted to the number of degrees fpecified. But this heat plainly did not operate in melting the ice, for then it should. have produced that effect at the end of the first half hour, when 7 or 8 degrees of heat must have entered the ice; whereas, that effect was not produced till the end of 23 half hours, when, by calculation, 140 degrees of heat, and upwards, must have fucceffively paffed through that fubftance. This heat then. did not act fenfibly: no; it was latent in the ice, and abforbed by it.

It may probably be faid, that the heat communicated by the air did not enter into the ice, but was repelled by it: but this cannot be; for, by experiment, a quantity of warm water being poured upon ice, that fubftance, in a manner, inftantaneously melts, without repelling, in the smallest degree, the heat that is thus forced into it.

By the theory of latent heat are explained the curious phenomena of artificial colds produced by mixture, as of fnowwater and falt: when these two are mixed, the fenfible heat is converted into latent, therefore the mixture must be fenfibly colder; at the fame time, the latent heat operates its ufual effect in keeping the mixture fluid, which would otherwife have a tendency to consolidate.'

The fame doctrine is again introduced under the head of vaporation. To be fatified, fays our Author, about the abforption of latent heat, by fluids that have attained the vaporific point, I put a fmall quantity of water into a phial closely corked, and expofing it to a fand heat, foon brought the temperature feveral degrees above the boiling point, which I could eafily effect, as the preffure made the fluid capable of receiving greater acceffions of heat. The fteam which arofe could not have vent, fo that upon taking out the cork, after an interval, in which all the water might have been converted into steam, I expected the whole would immediately disappear and be changed into vapour, which, as I imagined, would rufh forcibly out of the phial. This did not happen. Upon taking off the mechanical preffure, an ebullition and agitation of the water enfued, during which a portion of that fluid rushed out of the phial along with a quantity of fteam. The remaining water funk down to the boiling point, though before it had been confiderably above it. What then became of this quantity of heat? Was it annihilated? It does not appear in the water, though the minute before it acted fenfibly in it, by elevating the liquor in the thermometer feveral degrees above the boiling

point. That fenfible heat is converted into latent, and, though it no longer appears to act fenfibly, refides in the water. The following experiments are equally decifive upon this fubject:

A very large quantity of water being put into Papin's digefter, was exposed to the action of a violent fire, which foon brought the temperature 300 degrees above the boiling point; a degree of heat, of which water is fufceptible under great mechanical preffure, as in a veffel of this kind. Aftet confining the fteam for a long time in fuch an increase of heat, I naturally judged, that, upon admitting the air, or giving vent to the obftructed fteam, the whole mafs of water would inftantaneously evaporate. But here too, as in the former experiment, I was deceived; for, though, upon removing the preffure, a quantity of fteam burft out of the vessel, with fuch impetuofity, as to rattle several times against the cieling of the room in which the experiment was made; yet, by far the greater part of the water remained in the veffel; and what fo remained, almoft immediately funk to the boiling point, that is, 300 degrees delow its temperature at the time of removing the preffure. This heat must certainly have been abforbed by the water, and, from its acting fenfibly, have been converted into a latent form. Nothing else could have produced fo inftantaneous a change.'

The general obfervations on the theories of mixture, and the Appendix, contain nothing, but what must be very familiar to every one who is acquainted with chemical fubjects,

ART. XI. Voyages and Travels through the Ruffian Empire, Tartary, and Part of the Kingdom of Perfia. By John Cook, M. D. at Hamilton. 8vo. 2 Vols. 12 s. Boards. Edinburgh. 1770. Sold in London by Dilly, &c.

TH

HOSE whom bufinefs or pleasure has carried into foreign countries, feem, too frequently, to imagine, that it is incumbent on them to lay an account of their travels before the public; without queftioning whether they have the capacity to felect thofe particulars which are of fufficient value to awaken a general curiofity and attention; or whether they have the talents to exprefs them with propriety. All matters that have affected themselves, they conceive must be interesting to others. Heroes of each little tale, and important in their own opinion, they forget, that to the bulk of men they are unknown, and in a ffate of obfcurity. Their vanity does not permit them to fupprefs their journals; and, while they are Courting applaufe, they expofe themselves to ridicule.

Amidst the load of frivolous and abfurd details which Mr. Cook has prefented to his Reader, few facts or obfervations

occur,

D.

occur, that are of real confequence. If he chances to ftumble on a fubject that is interefting in itfelf, he is unable to explain. it in a fatisfactory manner. Some faint glimmerings of light he has, indeed, thrown on the hiftory of Ruffia; but thefe point to nothing great or conclufive. His relations are neither entertaining nor folid; and, indicating great weakness of mind, and a total ignorance of the language in which he writes, they either excite our pity or contempt.

One of the most unexceptionable articles in his work, is the account that is given of the manners of the Perfians; and, for this reafon, we fhall extract it for the entertainment of our Readers.

The Perfians, fays Mr. Cook, are naturally a very agile, lively people, the generality of their men are middle fized, rather of the fmaller kind, but very well made, tawny, blackeyed, with black hair, Roman nofed, and thick lipped. They all wear high caps gathered at the tops, which are tapering; they love the red colour, becaufe their foldiers caps are of that colour, and therefore they are called Kifelbafhee, or red heads. Their coats and vefts are fhort, and they wear long drawers and hofe made of cloth; in place of fhoes they wear univerfally flippers, with longer and more tapering heels than those wore by our British Ladies; which make them appear, in standing or walking, as if they had no mufculous pofteriors; because they are forced to ftand very erect.

Their foldiers confift chiefly in horfe; I have feen foot alfo; and they are esteemed, justly, I imagine, the best horsemen in the world. They have a fingular way of managing their horfes: they ride at a gentle trot, or walk them; but as they are not regular, they very frequently run off at a full gallop, and at once ftop their horfes; then pufh on, turning nimbly, frequently to the right or left fide, as the rider thinks proper. If they are near a steep low hill, they love to run up it as faft as the horse is able. When they arrive in their camp, they cover their horfes over with cloths three or four folds thick; then they tether their horses by the hinder feet, keeping them at a diftance; fo that they cannot eafily lie down; they then place cut-ftraw, or hay at fuch diftance, that the horfe can but get to it; fo that the beaft is, as it were, conftantly upon the stretch. They feed them twice daily with good barley, with which we were obliged to feed ours, which purged them fmartly for two or three days at firft; but it had a good effect, in making them very clear-fkinned. The Persian fol diers rub down their horfes frequently through the day: they are fonder of their horfes than of their wives.

By the Mahometan law, the Perfians can, and frequently do, marry four wives, and are at liberty to keep as many con

cubines

cubines as they pleafe. The world cannot produce greater flaves than the Perfian women are to their husbands. We were told, that a husband may chastise his wife, but must take care that his feverity does not prove the cause of her death; for if, upon enquiry, it proves to be fo, and the wife has relations who can profecute the murderer, the judge delivers the criminal to the relations of his deceased wife, who never fail to put him to death after the fame manner he killed his wife: this, however, is not always the cafe.

The women in Perfia are well enough proportioned; but I was informed they were not very beautiful, having had but few opportunities of feeing them myfelf. At Cura I one day faw an elderly woman dreffed in a ragged filk gown, whom hunger had forced into our camp, followed by two young girls, who paid her great respect. As fhe paffed through, the carefully picked up fome barley out of horse-dung and eat it; at which one of our dragoons would have beaten her, if I had: not prevented him. The Prince having been informed of her diftrefs, caufed feed her and her attendants, as long as we ftayed there. She faid, that fhe was well born, and had been married to a Khan; but that her family happening to fall under the Shach's displeasure + was utterly extirpated, and that none remained with her but the two girls, who never would leave her. This woman never had been a beauty. I have feen many girls, especially at Reshd, who were very beautiful; but I was informed that these were Georgians.

One day, paffing by a house out of the city, five or fix beautiful girls appeared at the door uncovered, and feemed to be very merry: they laughed, and made fome figns, as it were, inviting my comrades and me to go into the house; and I was told by others, that I was not miftaken, for they were common

to any.

I once faw a few girls who were kept by one of the Generals of the Perfian army, look out of a tent uncovered, as we paffed by; but I was told, that if their Lord knew that they had exposed themselves, he would have punished them most feverely. They were young, very pretty, and faid to be Georgians. I was informed that the Perfian women, in general, would fooner expofe to public view any part of their bodies

than their faces.

• One of the British merchants at Refhd told me, that one morning very early, as he was walking by a burial place, he there faw a very comely young woman fitting in her shift, be

Our Author accompanied Prince Galitzin in his embaffy to Perfia. The famous Nadir Shach,