in the former years, fo that, in the greatest cold of the winter 1785, it had arifen to 9.023. I waited to fee it defcend in the fpring; but, from the first day of May to the last day of June, notwithstanding the varieties of temperature, it has continued at 9.026 to 9.028. The variation has therefore been 0.022, about the fifth of a degree, and the mean height is about 9: according to Fahrenheit's fcale the heat is 201203 nearly, and the variation, about half a degree. It is not eafy to reason on these experiments in our limited circle; but, were the alternation of heat and cold once established, it would greatly influence our reafoning on thefe fubjects, and give a new appearance to the fyftems of philofophy. The more modern philofopher may, perhaps, already catch the hint, and fee, in the warmth of fummer, heat extracted from the earth, instead of being imparted by the fun.

In our purfuit of difcoveries in meteorology, a fcience though long cultivated, ftill in the most imperfect ftate, we have often had occafion to mention the labours of father Cotte. Our philofophical readers need not be informed that he published, in 1774, a treatife on meteorology, which included what was then known. His fubfequent labours have been occafionally communicated to the public, and, with fome new effays, have been lately collected: we fhall find no more fuitable place to give a short account of their contents, for the various effays of thefe two quarto volumes are intimately connected with the subjects of this sketch. Since our author's publication in 1774, the establishment of the Royal Society of Medicine at Paris, who have particularly attended to this branch of science, and of the Meteorological Society, under the aufpices of the elector Palatine, as well as the numerous correfpondents of the good father, have greatly increased our stock of knowledge on these fubjects. We may confider the diurnal, and monthly variation of the magnetic needle, by the affiftance of these obfervers, as almost demonftrated; the lunar period of 19 years, attended with a return of fimilar feafons, rendered highly probable; and even the fubordinate periods of 4 and of 8 or 9 years, as established on a foundation not wholly vifionary. The diurnal periodical variation of the barometer, which Van Swinden fufpected, feems to be also in some degree confirmed.

But to return to the volumes before us: the first memoir, in this collection, relates to the utility of meteorological obfervations, and to the most convenient method of reducing them, with the result of those made at Montmorency during thirteen years. The obfervations of feveral foreign philofophers are alfo compared and examined with care: fome of father Cotte's own errors, pointed out by others, are acknowledged; and, inftead of fhowing any displeasure, he modeftly remarks, that he fears his correspondents have treated him with too much complaifance.

The objects of the second memoir are heat and cold, the pro

bability

bability of a central fire, the difficulties attending this fyftem, and the degree of heat which the human body can bear. I he influence of the atmosphere on vegetation, and the probability of affifting the farmer, by carefully attending to the appearances of a change in the weather, are examined in another memoir. The author has collected whatever has been faid on the subject by different obfervers, and added his own remarks,

The fourth memoir is on the influence, which the moon may have on the atmosphere. Our author enquires whether from the combinations of the variations of the atmosphere, with the different pofitions of the moon, we can draw any conclufions, which mark a decided action of this planet, on the mafs of air, which furrounds us. He quotes feveral philofophers who are of opinion, that fuch influence exists; and, with M. Toaldo, he believes in the period of nineteen years. The agreement in the temperature of the weather, every nineteen years, from 1777 back to 1701, is pointed out from the obfervations of the late M. Du Hamel. There is scarcely any difference in the temperature of each corresponding month: the drought and moisture, which prevailed alternately, were the fame in anterior and correfponding years. The years 1778, 1779 and 1780 were alfo fimilar to the refpective years of the former period; but the eclipfes return at the end of eighteen years.

The fubfequent memoir is on the natural electricity of the atmosphere, from P. Cotte's own obfervations. He treats alfo on conductors and their neceffary elevation, enquires into the different quantities of fluids evaporated, according as they are placed in a free current of air, in a vacuum, or in veffels of different heights. From thence he proceeds to the principles of hygrometry, and particularly to the experiments of M. de Luc: he defcribes different hygrometers, compares the various instruments, and gives a table which contains the clements of the construction of the different ones, which he has made at Montmorency. In the memoir on the aurora boreales, he feems to think it difficult to give certain proofs of the analogy between these phoenomena and electricity. The effects of thefe aurora on the magnetic needle, which he examines at length, do not prove, in his opinion, their connection with electricity.

Four memoirs follow on the thermometer, and five on the barometer. The former inftrument he examines particularly; but the newest and most important part of this difcuffion is the obfervations on the improvement of thermometers, and the propofal of placing them more fuitably and conveniently to render the obfervation exact. On the fubject of the barometer he fpeaks of its conflruction, and the attemps to render the fcale more perfect. He purfues it, by giving different opinions on the caufe of its variation, by defcribing the prognoftics to be drawn from examining this inftrument, and the in

fluence

Auence of the lunar points on it. Tables relative to these two laft circumstances are fubjoined. The fourth is on the use of the barometer in meafuring heigths and depths. The fifth contains the facts relating to obfervations on, and the variations of the barometer, as well as the electrical property of the mercury which it contains.

One of the most interesting objects to philofophers is the magnetic needle, whofe property has extended, fo materially, the knowledge and dominions of man. Its course has been examined by different obfervers, and their discoveries; and our authors own are contained in four memoirs. In the first he defcribes the mariners compafs and the different methods of fufpending the needle: in the fecond, he establishes the connexion between magnetifm and electricity, followed by fome details on the declination of the needle, in different latitudes: in the third he offers the refult of obfervations made on the magnetic needle in the Gatinois by M. Dù Hamel, and by himfelf at Montmorency, for a series of years, to afcertain the influence of different temperatures on it: in the laft, he collects all the obfervations on the diurnal and periodical variation of this inftrument. Hevelius fufpected, fo early as 1682, that the magnetic needle had its periods of declination, fometimes to the Eaft, fometimes to the Weft; but a diurnal variation has been alfo obferved, which we have formerly copied from P. Cotte's memoir; fo that we fhall now confine ourselves to the more diftant periods.

The increase of declination begins in October, or towards the autumnal æquinox, and is at firft flow: it begins to be more confiderable in January, and is in its full force in February and March. It relaxes a little in April and May; is weak in June; a little stronger in July, to decline again in Auguft; from whence it gradually decreases, and, in September, the diminution is the greateft. These obfervations coincide with the discoveries of M. Swinden.

The second volume is concluded by a collection of extracts and obfervations, made at more than one hundred different places, and as it is the most exact, fo it is the most extenfive collection of obfervations, which has ever been published. Under each city, Father Cotte gives the authorities on which they are founded, and among them, we find the first philofophers on the continent, who have added what obfervation, reading, or the most extenfive correfpondence and communications have fuggefted. The particular facts occur in the different volumes of the Memoirs of the Royal Society of Medicine.

Among the obfervations, we remark particularly those of M. Beauchamp, the aftronomer at Bagdat, whofe affiduity and attention we have already had occafion to notice. They fill forty pages, and are accompanied by fome curious reflections on the climate of Bagdat, and particularly on the south wind, -styled feravanfum, or poifoned. This wind burns the face and almoft takes away the breath; it is fometimes fo fcorching,

that

that it deprives trees fuddenly of their leaves. It has been long known that this wind was mortal in the defart, for an hundred leagues round Bagdat, but it is not dangerous in the eity. Its effects are fudden, but it is felt fome time before its actual arrival, and avoided by laying with the face to the ground. It paffes over the caravan like a bullet, in a right line, and will kill a man, while one, on either fide, fhall efcape. The body of the perfon ftruck becomes black, and he does not live fix hours. It is pretended, that it fome times paffes over the port of Bagdat; and it is certain, that not only in the defart, but even under the walls of the city, it is fatal. It feems to be a blaft of phlogiflicated air, but is not rapid in its progrefs, fince an account is given of fome Arabs, who with M. Beauchamp, efcaped it by the fwiftness of their horfes. It ceafes in September; and, from this time to the beginning of July, the climate of Bagdat is faid to be very wholefome.

The medical topography of Montmorency is also curious. Its population amounts to 1580: one in thirty-four dies annually, and the average proportion of birth to a marriage is five. From fourteen to forty years of age the proportion of boys and girls, is nearly the fame: before that period, the boys are about one-tenth more numerous; and the proportion of births is thirteen boys to twelve girls.

We fhall conclude our account of P. Cotte's labours by a fpecimen of the manner, in which his obfervations are publish ed. We shall take it from his Meteorological Obfervations made at Laon, by order of the king for the month of January 1790.' The temperature of this winter, he obferves, forms a fingular contraft to the laft. The thermometer has fcarcely funk below froft: though the rains have neither been frequent nor copious, the air has always been moift, from frequent fogs. Vegetation has not been interrupted: anemonies have been in bloom, violets in bud, and the buds of fruit trees are large. Wheat is ftrong, and far advanced for the feafon.

The temperature correfponding to the different lunar points. follows, and the next object is the temperature of the month in the years of the lunar period correfponding to the prefent thefe are 1733, 1752, 1771. We own the refemblance in this month is not striking, nor are the temperatures of these years very confiftent: the fimilarity confifts in the wet weather, with the barometer above its mean height. We fhall felect only the different quantities of rain, which are four lines and a half, eleven lines, eighteen and two-third lines refpectively, and twenty-one and a half lines for the prefent month. The laft number perhaps ought to be reduced to fifteen and a half, because the evapora tion comprehended in the rain of the month feem not to have been confidered in the former years.

Father Cotte has alfo publifhed the continuation of his Obfervations on the Variation Compafs of M. Coulomb for the year 1789. The greatest variation was on the 27th of March,

7

with

with an aurora borealis, viz. 11° 24'; the least on the 16th of July, 4o 20'. The needle feemed to have a tendency to decline from the north, from eight in the morning to two in the afternoon, and to return to it in the fubfequent interval. The greatest agitation of the needle was obferved, at eight o'clock in the morning. Thefe obfervations confirm what occurred in the preceding years.

While we are on this fubject, we must not omit a new meteorological institution at Turin. The first part of an annual volume appeared laft year, entitled La Specola; Giornale d'Obfervazioni Meteorologiche. This Journal is the refult of the labours of a meteorological fociety, and compiled by G. D. Beraudo. The preface is defigned to explain the plan of the work, and, in it, M. Beraudo endeavours to point out the importance of the science, and the advantages which occur, at Turin, for its improvement. The obfervations are diftributed in four tables for each month: the three first are divided into feven columns, and give, at three different times of the day, viz. at feven in the morning, two in the afternoon, and nine in the evening, the height of the thermometer, in degrees and tenths of a degree; the height of the barometer in. inches, lines, and hundredths; the direction and force of the winds; the degrees of moisture and drynefs in the hygrometer of Sauffure; the electricity of the atmosphere, measured by the divergence of threads, and the appearance of the heavens. This laft circumftance, though generally omitted, is a very important one, but it requires much attention; a peculiar language to convey a proper idea of the fingular appearances of the clouds and of objects feen through the air, in the different flates; a language that must be varied in almost every climate. The fourth table is divided into eight columns, in which are marked the days of the month, thofe of the moon, the lunar points, the quantities of rain and fnow, with the quantities evaporated, and three columns of abridged marks, defcriptive of the different meteors. The recapitulation of the refults follows, and this part contains not only the refults of the tables, but different facts refpecting the abundance or defect of eatables, the height of the Po, the difcafes of men, of animals, &c. A fhort relation of the epidemics which occurred at Turin, in Sardinia, and Chambery, follow, with a fuccinct account of the variations of the thermometer and barometer in the capital of Savoy, by Dr. Daquin.

FOREIGN ARTICLE.

Suite des Confeffions de J. J. Rouffeau, formant le fecond Supplement à la Collection de fes Oeuvres. 3 Toms. 12mo. Paris. IT is no longer neceffary to give an account of the former works, or of the perfon of Rouffeau: they are well known, and the public opinion has afcertained their real value with fufVOL. LXX. Aug. 1790. fcient

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