Sir D. Brewster on the Law of Daily Temperature. 343 



pole being -f 1° Fahr., and that of the western — 3|°, and 

 that they were nearly coincident with the magnetic poles of 

 the earth. These views have been adopted by Humboldt, 

 Erman, Kupffer, Dalton and others ; and we have no doubt 

 that we shall be able, by means of the accurate meteorological 

 observations which are now making in different parts of the 

 world, to fix more accurately the position of these remarkable 

 points, and to determine whether or not their connexion with 

 the magnetic poles is merely accidental. 



This remarkable distribution of heat over the earth's sur- 

 face, or rather in our atmosphere, is connected with the un- 

 equal distribution of heat over the year. In the cold meri- 

 dians we have a hot summer and a cold winter, whereas in the 

 warm meridians the difference between the summer and the 

 winter temperature is greatly diminished. In order to express 



65°*3 

 this conjoined effect, Humboldt adopts the form 51°*1 



38 *7 



adding the signs of + and — , according as the numbers 



+ 65°*3 

 are above or below zero. Thus + 51°'l expresses 



the temperature of Paris ; the number 51°*1 being the mean 

 annual temperature, 65 0, 3 the mean temperature of summer, 

 and 38*7 the mean temperature of winter. This arrangement 

 of the temperatures has, however, so much the appearance of 

 a mathematical formula, that we conceive it would be more 

 natural to place the numbers thus: + 65*3, + 51°*1, + 38 0, 7, 

 or max. 65°*3, mean 51 0, 1, min. 38 0, 7, the mean temperature 

 occupying the middle place between the two extremes, and 

 the negative signs alone being prefixed to the numbers when 

 they are below zero. 



In treating of the cause of the inflexion of the isothermal 

 lines, Baron Humboldt has endeavoured to show, by very inge- 

 nious arguments, that the form, the extent, and the altitude of 

 the continents, and their relation to the polar ice, are the prin- 

 cipal causes of these inflexions. We are not prepared either to 

 controvert or to admit the accuracy of this explanation, which 

 we have no doubt will meet with a ready and a general accept- 

 ance ; but when we look at the system of isothermal curves 

 surrounding the poles of revolution, and mark their coinci- 

 dence with the magnetic poles of the earth, and their simi- 



where T is the mean temperature of any place whose distance from the 

 two cold poles is § and V, t the mean equatorial temperature, r the mean 

 temperature at each of the poles of maximum cold. The distances § and V 

 are found by the formula for D given above. The exponent n is about 

 five-eighths, when the formula represents the most accurate observations." 



