METEOROLOGY.

5m

“ If the elevation of a country al>ove the level of the sea pro-ceeds at a greater rate than six feet per mile, we must, accordingt°Mr. Kirwan, for every 200 feet of elevation diminish the an-•Hud temperature of the standard in that latitude as follows: if theOvation be at the rate of G feet per mile, of a degree ; 7 feet ^ ;13 feet, T 4 5 ; la or upwards, f. For everv 50 miles distance fromAil: standard ocean, the mean annual temperature in different lali-tl| des is to be depressed or raised nearly at the following rate :

From Lat. 70° to 35° depressed f of a degree.

35.

30.

.7

.0

25 raised.-j

20 . 1 -

10.I

"The cause of the heat of the atmosphere is evidently the sun’sr ays. -The heat which they produce i.s less according as they fall°hliquelv ; hence the temperature constantly diminishes from theequator to the pole, because their obliquity constantly increases"jilli the latitude. Hut if the heat depended on the solar rays“'One, it would disappear in the polar regions during winter, whensun cea««< to rise. This, however, is by no means the case ;:! le mean temperature even at the pole is 31°; and we find withinarctic circle as hot weather as under the equator. The reasonfins is that the sun’s rays heat the earth considerably duringSummer: this heat it retains and gives out slowly during winter,? I1( J thus moderates the violence of the cold ; and summer returnsdjdove the earth has time to be cooled beyond a certain degree..! ms is the reason, that the coldest weather does not take place atm winter-solstice, but some time after, when the temperature of1( -“ earth is lowest; and that the greatest heat takes place also someconsiderable time after the summer-solstice, because then the?'"perature of the earth is highest. For pure air is not heated byle solar rays which pass through it; but acquires slowly the tem-perature of the earth with which it is in contact. This is the rea-m" wl, y the temperature decreases according to the elevation’ >ov e the level of the sea. Since the atmosphere is heated byontact with the superficies of the earth, its temperature must de-* 'Td upon the capacity of the superficies for receiving and trans-^..“Img heat. Now this capacity differs very much in land anda ler. Tand, especially when dry, receives heat with great readi-jjf?> but transmits it through its own substance very slowly. Dr.

s found, that, in 1724, when the air and surface of the earthSi e, 'e both at 88°, a thermometer placed only two inches below the•pj. ce stood at 85° ; another 1G inches below at 70°; and another

j( mches deep at 68°—The earth, at about 80 or 90 feet belowUp Slll 'face, constantly retains the same temperature ; and this is® r b’ equal to the mean annual heat of the country. Hence thea ean annual temperature of any country, may be found pretty^f-'braidiy by examining the heat of deep wells or springs.

a jw receives heat slowly on account of its transparency; but

i, v , ff does receive is very quickly carried through the wholellj Ss * Laud is often heated and cooled to a much greater degreelie-'! sea ' s - Hr. Raymond often found the earth near MarseillesI to 170°, but never found the sea above 77°: in winter the

1 was often cooled down to 14°, but the sea never lower than

H ' The sea-atmosphere, therefoie, ought to preserve a much(i , le unifo™ temperature, than the land-atmosphere; and weter t; s to he the case. The cause of the greater equability of wa-si u l 111 land is evident. In summer the surface of the sea is con-Sl >rfa- celled down by evaporation; and in winter, whenever the"vity tC i ! s c °oled, it descends to the bottom from its increased gra-gopg’iie its place is supplied by warmer water. This processiia s , 011 continually, and in winter is over before the atmosphere“ -pi ee,! a hle to cool down the water bevorul a certain degree.tak es ' es ? observations enable us to explain" the difference whichaboypl, ce between the annual temperature of the atmospherefro lri • | e ocean, and that of places at some considerable distanceh'eaii -* the sea is never heated so highly as the land, thev *orl4* U . n ? mer - ,e,n P eratur ‘ ! at sf ‘ a may be considered all over thethe sn, a > S 0Uer than on land. During winter, when the power ofthe a i r ' s ra y s 111 a great measure ceases, the sea gives out heat toherat lll . rnilc b more readily than the earth : the mean winter-tem-c °Untri e ’ ! herefore > at sea, is higher than on land; and in cold' a "tes tl 'c ^‘herence is so great, that it mare than eounlerba- jlVoi 16 c difference which takes place in summer; so that in high I111 —No 142. '

latitudes the mean annual temperature ought to be greater thanon land. Accordingly from lat. 70° to 35°, to find the tempera-ture of a place, the standard-temperature for the same latitudeought to be depressed one-eighth of a degree for every fifty miles-distance; for the cold which takes place in w inter always increasesin proportion to the distance from the standard. At a less dis-tance than fifty miles, the temperatures of land and sea are soblended by sea and land-winds, that there is little diffeience in theannual mean. In lower latitudes than 30°, the rays of the sun,even in winter, retain considerable power; the surface of the earthis never cooled very low; consequently the difference betweenthe annual temperatures of the sea and land become less. As weapproach nearer to the equator, the power of the solar rays duringwinter increases so that the mean winter-temperature of the land-atmosphere approaches nearer and nearer to that of the sea, tiil atlast at the equator it equals it. After we pass lat. 30°, therefore,the mean annual land-temperature gradually exceeds that of the'sea more and move, till at the equator it exceeds it a degiee forevery fifty miles distance. Such then, in general, is the methodof finding the mean annual temperature over the globe. Thereare, however, several exceptions to these general rules,” enu-merated by Dr. Thomson, of which we shall only quote one ortwo of the principal. “ Small seas surrounded with land, at leastin temperate and cold climates, are generally warmer in summerand colder in winter, than the standard ocean, because they are agood deal influenced by the temperature of the land. The Gulpliot Bothnia , for instance, is for the most part frozen in winter; butin summer it is sometimes beatedto70°; a degree of heat neverio be found in tlie opposite part of the Atlantic . The Germansea is abo'’e three degrees colder in winter, and five degreeswarmer in summer, than the Atlantic. The Mediterraneansea is, for the greater part of its extent, warmer both insummer and winter than the Atlantic , which therefore flows intoit. The eastern parts of North America are much colder thanthe opposite coast of Europe , and fall short of the standard byabout 10° or 12°, as appears from American Meteorological Ta-bles. The causes of tiiis remarkable difference are many. Thehighest part of North America lies between 40° and 50° of N. Jat,and 100° and 110° of \V. ion. of London ; for there the greatestrivers originate. The very height, therefore, makes this spotcolder, than it otherwise would he. It is covered with immenseforests, and abounds with large swamps, which render it incapableof receiving any great degree of heat; so that the rigour of winteris much less tempered by the heat of the earth than in the oldcontinent. Islands are warmer than continents in the same degreeof latitude, and countries lying to the windward of extensivemountains or forests are warmer than those lying to the leeward.Stones or sand have a less capacity' for heat than earth has, whichis always somewhat moist; they heat or cool, therefore, to agreater degree. Hence the violent heat of Arabia and Africa,and tlie intense cold of Terra del Fuego. It is probable that thevariations of the barometer, as well as those of the thermometer,are susceptible of what we may term a local character for eachtract or country differing in climate. This will be most readilydiscovered by the following mode of investigation: preparea sheet of paper ruled in squares with pale ink; the horizontallines agreeing with the inches and decimal divisions of the scaleof the barometer, the perpendicular, which may' be about twice asdistant, representing divisions of time. It will be convenient toconsider each line as denoting midnight, and to mark the days ofthe month at the top of the columns thus defined. On this scalelet the several notations of any register of the barometer be setdown by means of a dot for each, placed in the part of the scalewhere it may point out the time and the elevation. The desirednumber of notations thus made, a curve may be drawn through,the series of dots, which will represent at one view the course'ofthe barometer for the time. It will be found, on comparing anumber of these curves, that they characterise, in a certain degree,,not only the latitude and season, but the locality of the observa-tions. So that although the most obvious resemblances may betraced in different years of the same register, yet the general ap-pearance of registers from different climates, will be found to differin all respects. In this way may be seen at one view both thecorrespondence between the latitude or elevation above the seaof any place, and the range at that place ; and the coincidence be-tween the movements of the barometer, and the other phenomena:

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