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cd neck of land. It is purely volcanic, and in every part of it are feen huge columns of bafaltes, placed almoft vertically, except towards the lower part of the point of land, where they are inclined at different angles. The pentagonal form prevails, and the ftone itself is of a fine grain and dark colour; it ftrikes fire with fteel.

The mountain is covered in feveral places with a reddish volcanic earth infoluble in acids, which I confider as a true puzzolane earth, and have accordingly employed it with great fuccefs in repairing the royal cifterns; the cement I compofed of it has hardened perfectly, and retains the water exceedingly well, though made with

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We have visited the Magdalen Isles, diftant about a league and a half from Goree: they are compofed entirely of immenfe columns of bafaltes, like thofe of the Vivarais, and of Auvergne: the fea, by breaking with violence against thefe columns, has formed in fome places vaft chafms, which have laid open the interior appearance of them to a great depth. It is very dangerous to come too near these vaft and deep precipices, where the fea breaks with dreadful noife. One of my companions, as he was contemplating this fublime fpectacle, was reached by a wave which threw him down; but luckily, though much bruifed, he got up and made his escape before the arrival of the next wave.

In these Magdalen Islands, I meafured three Baobab trees *, each of which was more than fixty feet in

circumference, and the names of a great many French and English tra vellers were engraven on the bark.

It is not true that the electrical machine cannot be excited in the torrid zone: ours produced abundance of fparks. The thermometer, on the 15th of January, when we arrived, ftood at 16° above o. After that it rofe to 23° and 24°, when it again defcended, and is now at 18°; but in the fun it gets up to 40° f. It is true, that the fun paffes directly over our heads, but luckily there reigns here almoft continually a fine fresh breeze, which moderates his heat. The air is very pure at Goree, except in the rainy feafon, which gener ally begins on the 3d or 4th of July, and continues three or four months; in that time there falls about thirtyfix or forty inches of rain, which ferves for the whole year. However, I have feen it rain twice fince our arrival, but every body was aftonished at it; and there are old men here who pretend that their fathers had feen fnow fall; but this is hardly credible, as the thermometer, for a long time, has not been lower than 12 (54° F.).

Our negroes here produced fire by whirling round a bit of stick hole of a piece of wood, and lighting at it a fort of tinder made of the down of a thistle. The fea abounds in fish on thefe coafts, and I have feen three hundred pounds of fresh fish fold for a fmall knife with a black handle, such as in France might be bought for two pence.

An

*Adanfonia Baobab. Lin.

The French make ́use of Reaumur's thermometer. The corresponding degrees in Fahrenheit are nearly as follow: 169 R. 60o F. 24° R. 76° F. 18° R. 64° F. 40° R. 104° F.

An Account of fome new Experiments on the Production of Artificial Cold. In a Letter from Thomas Beddoes, M. D. to Sir Jofeph Banks, Bart.

P. R. S*.

DEAR SIR,

MR

Oxf. May 2. 1787. RWALKER, apothecary to the Radcliffe Infirmary here, has been engaged upwards of a year in a feries of experiments on the means of producing artificial cold, feveral of which feem to me to be very remarkable, and fuch as, confidering their novelty, and the attention which has lately been paid to this fubject, I flatter myself will be found to deferve a place among the Tranfactions of the Society over which you prefide.

Mr Walker, in his firft experiments, found, as Boerhaave had done before him, that fal ammoniac, as well as nitre, well dried in a crucible, and reduced to a fine powder, will produce a greater degree of cold than if they had not received this treatment. But Boerhaave, by fal ammoniac, lowered the temperature of water only by 28°; whereas Mr Walker obferved this thermometer to fall 32°, and when he used nitre 19°. It occurred to him, that the combination of thefe fubftances would produce a greater effect than either feparately: and he found that this was really the cafe. A propofal for freezing water in fummer, mentioned by Dr Watfon (Effays, III. 139.) determined him to attempt the fame thing in this way. Accordingly, April 28, 1786, the thermometer standing at 47°, he made a folution of a powder, confifting of equal parts of fal ammoniac and nitre, in a bafon, by means of which he cooled fome water, contained in a glafs tumbler, to 22°. To this he added some of the fame powder, and immerfed two very small phials in it; one containing boiled, the other unboiled water; when he foon found the water in the phials to be frozen, the unboiled freezing first.

Having obferved that Glauber's

falt, when it retains its water of cryftallization, produces cold during its folution, he thought of adding this to his other powers, and July 18, 1786, reduced the thermometer 46 degrees. In this experiment the following proportions were used: the temperature of the air being 65°, to water four ounces, at 63°, were added, Of fal ammoniac 3 xi therm. funk to 32°, Of nitre 3 x to 24°, that is, 8°/ Of Glaub. falts 3ij-to 17°, that is, 7°

that is, 319

46°

In this way he froze water on a day fo hot that the thermometer in the fhade ftood at 70°. By first cooling the falts and water in one mixture, and then making another of these cooled materials, he funk the thermometer 64 degrees,

Aug. 28. The temperature of the air being 65°, half an ounce of rectified fpirit of wine was diluted with three ounces and an half of water, and immerfed in the fame frigorific mixture. When cooled to 24, it began to freeze. A quantity of the neutral falts, likewife cooled in the mixture, were put into the diluted fpirit, when the thermometer fell to - 4o, fo that the liquor was cooled 69 degrees.

Spirit of nitre, diluted in the manner defcribed by Mr Cavendish (Phil. Tranf. vol. LXXVI. part I.) having reduced the thermometer to -3°, fal ammoniac was added, upon which it fell to 15o.

Nitrated volatile alkali, during its folution in water, reduced the thermometer 35 degrees (from 50° to 15°); but the cold was not increafed by fal ammoniac or nitre.

F 2

Mr Walker's most remarkable experiment was made on the 21ft of March, 1787, when he found, that

* Phil. Tranf. vob LXXVII. Part U.

nitrous

nitrous acid, when poured upon Glauber's falt, produced effects nearly the fame as when it is poured on pounded ice; and that the cold, thus produced, is rendered ftill more intense by the addition of fal ammoniac in powder!

the largest pan. The third pan, containing the falts for the third mixture, was immerfed in the liquor of the fecond pan; and the liquor for the third mixture was put into wide-mouthed phials, which were immersed in the fecond pan likewife, and floated round the third pan. The fourth pan, which was the fmalleft of all, containing its cooling materials, was placed in the midst of the falts of the third pan.

Mr Walker, by many trials, difcovered that the best proportion of thefe ingredients is the following: Of concentrated nitrous acid, 2 parts by weight, of water 1 part; of this Of the materials for the mixtures mixture cooled to the temperature of to be made in thefe four pans, the first the atmosphere eighteen ounces, of and fecond confifted of diluted vitrioGlauber's falt a pound and an half lic acid and Glauber's falt, the third (avoirdupois,) and of fal ammoniac and fourth of diluted nitrous acid, twelve ounces. On adding the Glau- Glauber's falt and fal ammoniac, in ber's falt to the nitrous acid, thus the proportions affigned, diluted, the thermometer fell from 51° to -1°, or 52 degrees; and on adding the fal ammoniac it fell to -9°, that is full 60 degrees. Nitrated volatile alkali, employed instead of fal ammoniac, produced a cold rather more intense.

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By means of this mixture, in a very few minutes, in the elaboratery before the clafs, I froze fome fpirits above proof, diluted with an equal bulk of water; and another gentleman this day funk the thermometer 68 degrees.

On April 20, 1787, Mr Walker effected the congelation of quickfilver by a combination of thefe mixtures, without a particle of fnow or ice. When he began his experiment the temperature of the mercury was 45°, fo that, the freezing point of that metal being 39°, there were produced 84 degrees of cold.

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This experiment was performed as follows: Four pans, of fizes progreffively diminishing, fo that one might be placed within the other, were procured. The largest of these pans was placed in another veffel ftill larger, in which the materials for the fecond frigorific mixture were thinly fpread, in order to be cooled. The fecond pan, containing the liquor (viz. vitriolic a sid, properly diluted) was placed in

The pans being adjusted in the manner above defcribed, the materials of the first and largest pan were mixed: this mixture reduced the thermometer to +10, and cooled the liquor in the second pan to + 20; and the falts för the fecond mixture, which were placed underneath in the large veffel, nearly as much. The fecond mixture was then made with the materials thus cooled, and it reduced the thermometer to 3°. The ingredients of the third mixture, by immersion in this, were cooled to + 10°, and when mixed reduced the thermometer to The materials for the fourth mixture were cooled by immersion in this third mixture to about 12°. On mixing they made the mercury in the thermometer fink rapidly, and, as it appeared to Mr Walker, below - 40°. Its thread feemed to be divided below that point; but the froth occafioned by the ebullition of the materials prevented his making fo accurate an obfervation as he could have wished.

15o,

The reason why this laft mixture reduced the thermometer more than the third, though both were of the fame materials, and the laft at a lower temperature, Mr Walker imagines to have been partly, because the fourth pan had not another immersed in it to give it heat, and partly becaufo

the

the materials were reduced to a finer powder.

I fhould imagine, that mercury reduced to its freezing point will freeze more quickly than water reduced to its freezing point; because it appears, from experiments on their capacity for heat, that the latter of thefe bodies has fo much more latent heat in its liquid ftate; which greater quantity of latent heat muft, as it becomes sensible, more retard the congelation. I forbear to enumerate many variations of thefe experiments which Mr Walker has among his notes; but there is one mixture which, tho' its power is not equal to that which I have laft defcribed, may prove very ferviceable in experiments of this nature, on account of its cheapnefs. It confifls of oil of vitriol diluted with an equal weight of water: added to Glauber's falt, it produces about 46 degrees of cold. The addition of fal ammoniac renders it more intenfe by a few degrees. One remarkable circumftance occurred to Mr Walker, as he was endeavouring to ascertain the best strength of the vitriolic acid: he happened to be trying a mixture of two parts of oil of vitriol and one of water, when he observed, that, at the temperature of 35°, the mixture coagulated as if frozen, and the thermometer became stationary; but, on adding more Glauber's falt, it fell again, after fome little time, but fo great a cold was not produced as when this circumftance did not occur, and when the acid was weaker. The fame ap

pearance of congelation took place with other proportions of acid and water, at other temperatures.

Mineral alkali, when it retained its water of cryftallization, added to fome of thefe mixtures, heightened their effects: But when it had loft this water, it rather produced heat than cold; and the fame thing is also true of Giauber's falt. This circumstance leads us, in fome measure, to the theory of thefe phænomena. Water undoubtedly exifts in a solid state in cryftals; it must therefore, as in o ther cafes, absorb a determinate quantity of fire, before it can return to its liquid flate. On this depends the difference between Glauber's falt and fofil alkali in their different ftates of cryftallization and efflorefcence. The fame circumftance too enables us to understand the great effect of Glauber's falt, which, as far as I recolle&, has the greateft quantity of water of crystallization.

Thofe, therefore, who fhall choose to pursue the path which Mr Walker has opened to them, would do well to try combinations of falts containing much water of cryftallization; but they must take care left the effect fhould be diminished or deftroyed by the formation of compounds that fix a fmaller quantity of fire. It is, how ever, but justice to Mr Walker to obferve, that he has carried his experiments in this way very far, and with great ingenuity.

I have the honour to be, &c.
THOMAS BEDDOES.

Obfervations on the Structure and Economy of Whales. By John Hunter, Efq. F. R. S.; communicated by Sir Joseph Banks, Bart. P. R. S.

THE

HE animals which inhabit the fea are much less known to us than thofe found upon land; and the economy of those with which we are beft acquainted is much lefs underflood: we are, therefore, too often

obliged to reafon from analogy where information fails; which muft probably ever continue to be the cafe, from our unfitnefs to pursue our researches in the unfathomable waters.

The anatomy of the larger marine animals,

animals, when they are procured in a proper ftate, can be as well afcertained as that of any others; dead structure being readily inveftigated. But even fuch opportunities too feldom occur, because thofe animals are only to be found in diftant feas, which no one explores in purfuit of natural hiftory; neither can they be brought to us alive from thence, which prevents our receiving their bodics in a state fit for diffection. As they cannot live in air, we are unable to procure them alive.

As the opportunities of afcertaining the anatomical ftructure of large marine animals are generally accidental, I have availed myself, as much as poffible, of all that have occurred; and, anxious to get more extenfive information, engaged a furgeon, at a confiderable expente, to make a voyage to Greenland, in one of the hips employed in the whale fishery, and furnifhed him with fuch neceffaries as I thought might be requifite for examining and preferving the more interefting parts, and with inftructions for making general obfervations; but the only return I received for this expence was a piece of whale's skin, with fome fmall animals fticking upon it. From the opportunities which I have had of examining different animals of this order, I have gained a tolerable accurate idea of the anatomical structure of fome genera, and fuch a knowledge of the structure of particular parts of fome others, as to enable me to afcertain the principles of their economy.

Thofe which I have had opportunities of examining were the follow ing:

The Delphinus Phocæna, or Porpoife. The Grampus. The Delphinus Delphis, or Bottle-nofe Whale. The Balena Roftrata of Fabricius. The Balena Myfticetus, or large Whalebone Whale; the Phyfeter Macrocephalus, or Spermaceti Whale; and the Monodon Monoceros, or Narwhale.

The animals of this order are in fize the largest known, and probably. therefore, the feweft in number of all that live in water. Size, I believe, in those animals who feed upon others, is in an inverfe proportion to the number of the smaller; but, I believe, this tribe varies more in that refpect than any we know, viewing it from the Whalebone Whale, which is feventy or eighty feet long, to the Porpoife that is five or fix: however, if they differ as much among themselves as the Salmon does from the Sprat, there is not the comparative difference in fize that would at firft appear. The Whalebone Whale is, I believe, the largeft; the Spermaceti Whale the next in fize (the one which I examined, although not full grown, was about fixty feet long;) the Grampus, which is an extensive genus, is probably from twenty to fifty feet long ; under this denomination there is a number of fpecies.

From my want of knowledge of the different genera of this tribe of animals, an incorrectnefs in the application of the anatomical account to the proper genus may be the confequence; for when they are of a certain fize, they are brought to us as Porpoifes; when larger, they are called Grampus, or Fin-fifh. A tolerably correct anatomical defcription of each fpecies, with an accurate drawing of the external form, would lead us to a knowledge of the different genera, and the fpecies in each; and, in order to forward fo ufeful a work, I propofe, at fome future period, to lay before the Society defcriptions and drawings of those which have come under my own obfervation.

This order of animals has nothing peculiar to fifh, except living in the fame element, and being endowed with the fame power of progreffive motion as thofe fish that are intended to move with a confiderable velocity: for I be lieve, that all that come to the furface of the water (which this order of

animals

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