OF THE GLOBE. 203 



in many parts of the world, yet the observations with it have 

 commonly been guided by no settled principle, and are, there- 

 fore, frequently unfit for the purposes of generalisation. Phi- 

 losophers were satisfied with deducing a law of temperature 

 from theoretical considerations ; and disdained the humbler 

 and more laborious task of interrogating the mass of facts 

 which had been accumulated by zealous and active observers. 

 The first person who attempted to deduce from obser- 

 vation a general expression for the mean temperature, at 

 all latitudes, was the celebrated astronomer Tobias Mayer 

 of Gottingen. Assuming that the heat varies as the 

 square of the sine of the latitude, he obtained the formula 

 T — 58 -f- 26 X Cos. 2 Lat., in which 58 is the mean tempera- 

 ture of 45° of north latitude, and 26° the difference between 

 the temperature of that parallel and the Equator. M; Lich- 

 tenberg, the editor of Mayer's posthumous works, applied 

 this formula to 13 observations of mean temperature made be- 

 tween the Cape of Good Hope and Stockholm, and their 

 agreement was considered at that time to be remarkable. The 

 sum of all the errors was 26°.8, or a little more than 2° on each 

 observation; but as the errors in excess amounted to 22°. 3, 

 while those in defect were only 4°.5, it should have been ob- 

 vious that the formula was founded upon an incorrect as- 

 sumption. 



The formula of Mayer was implicitly adopted by Kirwan, 

 in his able work On the Mean Temperature of the Earth; and 

 has been more recently brought forward, as connecting toge- 

 ther, " in a most harmonious manner," the results of distant 

 temperatures, although the fine series of observations, collec- 

 ted by Humboldt, had demonstrated its inaccuracy, and pro- 

 ved, that even in the parallel of 63*, it erred in excess no 

 less than 9' of Fahrenheit. 



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