156 



METEOROLOGY. 



Meteorolo- neral view of the diminution of temperature from the 

 g. y ' Equator towards the Pole ; and though, in its present 

 form imperfect, as we shall afterwards show, it may, 

 by future corrections, become in time more accurate, 

 as well as more extensively applicable. 



The formula, as stated by Mr. Playfair in his Out- 

 lines of Natural Philosophy, is as follows. Let L be 

 the latitude of the place whose temperature / is requir- 

 ed, M the mean temperature of the parallel of 45, and 

 M-f-E the mean temperature of the Equator, then 

 /=M + E cos. 2 L. 



According to the observations collected by Mayer, 

 M=58, M + E=85, and consequently E=27. By 

 substituting these numbers, the formula becomes 

 /=58+27xcos. 2 L. 



When the latitude exceeds 4.>, 2 L is greater than 

 90, so that cos. 2 L becomes negative, or / is less than 

 58. The formula may be thus expressed at length. 

 Multiply the cosine of twice the given latitude by 27, 

 and add the product to 58 ; the sum will be the mean 

 temperature of that latitude at the level of the sea. 

 By this formula we have calculated the following ta- 

 ble, showing the mean temperature for every parallel 

 of latitude from the Equator to the Pole, expressed in 

 degrees of Fahrenheit's thermometer. The table, strict- 

 ly speaking, belongs to the subject of climate, which 

 will be considered at greater length under the article 

 PHYSICAL Geography ; but as it is also intimately con- 

 nected with the method of ascertaining the mean tem- 

 perature, and as we shall have occasion hereafter to re- 

 fer to it, in the course of this article, we have thought 

 proper to introduce it here. 



Table de- 

 duced from 

 Mayer's 

 formula. 



Mr. Leslie, in his Elements of Geometry, has express. Mcteorolo- 

 ed the above formula somewhat differently, and the gy- 

 results which he has deduced from it are also different. 

 He assumes the mean temperature of the equator to - 



be 29 centigrade, or 84 .2 Fahrenheit, and the mean tj,, n .i>r The 

 of the pole comes out 32. In all latitudes between formula 

 the equator and the parallel of 4-5, the mean tempera- still more 

 tures in Mr. Leslie's Table are rather less than those in inaccurate, 

 the above, and for higher latitudes somewhat greater. 

 It appears, however, that the modification of the for- 

 mula which he has employed, does not agree so well 

 with the latest observations, as the original expression 

 of Mayer, except in one case, where Mr. Leslie him- 

 self has applied it; nor do we find any satisfactory 

 evidence in support of his opinion, that the law, 

 as he has modified it, connects most harmoniously 

 the various results of observations made at distant 

 points on the surface of the globe. So far from 

 this being the case generally, we can find nothing 

 like harmony between the results of the Table and ac- 

 tual observations, even in that portion of the globe to 

 which philosophers, previous to Mr. Leslie's extension 

 of the law, considered the formula as applicable, viz. 

 bet een the parallels of Stockholm and the Cape of 

 Good Hope, and from the meridian of Stockholm west- 

 ward to the coast of America. In proof of this, we 

 shall extract from the meteorological observations col- 

 lected by Humboldttbr the purpose of determining the 

 isothermal lines, or lines of equal temperature on the 

 globe, the mean temperatures of a few places at the 

 level of the sea, and compare them with the standard 

 temperature as given by Mayer and Leslie, confining 

 ourselves to such as were determined with the greatest 

 precision, and from the greatest number of observa-- 

 tions. 



The only instances in the above Table, where there instances 

 is any thing like a coincidence between the result of of agree- 

 observation and Mr. Leslie's formula, are those of Edin- men be- 

 burgh and Rome, where the difference is exactly half a tw 

 degree; but it would surely be a very unwarranted ^^"'^1 

 stretch in the adaptation of facts to theory, to set up O i,, c rva- 

 two or three instances ot agreement against so many tions acci- 

 and such glaring discrepances as the Table exhibits, dental. 

 The mean temperature of Edinburgh is said to be 

 deduced from six years observations by Mr Play- 

 fair. We suspect there is an error in this statement, 

 as 47-8 is the mean of three years observation*, viz. 

 1797, 1798, and 1799, as given by Mr. Playfair in the 

 Philosophical Transactions But however this. m;iy be, 

 we are still disposed to regard the coincidence in this 



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