Fo% of the Mississippi, 4& 

 by Baron Humboldt, in his celebrated work on the Geography of 

 plants by comparing the climates of the old and new continents. 

 With a certain place in North America, whose mean annual tem- 

 perature is known, for example, Natchez (31° 28' lat. 18.2°* mean 

 temp.) the author makes a two fold comparison, viz. he first com- 

 pares with this place one in the old world, which lies under the 

 same degree of latitude ; the mean temperature of this last, com- 

 pared with that in North America, gives them the difference of 

 temperature. Secondly, he compares with it a place in the old 

 world, which has the same mean temperature, and this comparison 

 then gives the difference of latitude between the two places. But 

 as we cannot easily have for such a comparison, places in the old 

 continent, whose mean temperature, or geographical latitude, agrees 

 exactly with the given places of the new continent, the author has, 

 in each of these comparison?, made use of two places in the old 

 continent, from which the geographical latitude or the mean tem- 

 perature of the place is determined, that is to be compared with 

 one in North America. He must then, in order to institute a com- 

 parison with Natchez, first fix upon a place in the old continent 

 which lies under 31° 28' of latitude, and the mean temperature of 

 whieh should be known ; to obtain this, he compares Funchal, 32° 

 27', and Oratava, 2S° 25', and calculates from the difference be- 

 tween the mean temperatures of both places, the probable mean 

 temperature of 31° 28' in the old continent ; this is 20° 5', which 

 number compared to 18° 2' gives a difference equal to 2° 3'. Se- 

 condly, he must have a place in the old continent whose mean tem- 

 perature should be 18° 2' ; he obtains this place in the same man- 

 ner through a comparison between Rome, 15° & (41° 33' of lat.) 

 and Algiers, 20.1° (36° 33' of lat.)t 



The application of this formula in the present instance, will not 

 only make up for the want of observations, but will furnish the 

 means of making the comparisons with greater facility. From 

 five places on the sea-coast in different parallels of latitude, whose 

 mean temperature is known, we shall in this manner be able to as- 

 certain the probable mean temperature of those points on the coast 

 corresponding in latitude with those places in the valley of the 

 Mississippi, whose mean temperature has also been ascertained. 



.1911 



