*witli preliminary Observations on Climate. 547 



of the greatest desiderata in horticultural knowledge now is, a 

 similar knowledge of all other climates whence vegetable pro- 

 ductions are imported for cultivation, in order that their range 

 of temperature may, in like manner, be precisely ascertained. 

 But, notwithstanding the rapid advances of science, and the 

 accelerations of intercourse by steam or railroad communication, 

 this must require a lapse of years. In the mean time, some 

 approximation might be attainable, and rendered useful, by 

 improving on the following considerations. 



The astonishing power which causes once in twenty-four 

 hours a general movement, more or less, of the sap of vegeta- 

 tion, in that expanding in the tropics, as well as in that of the 

 humble inhabitants of the polar regions, is well known to be 

 derived from the solar rays. The effect of the latter is more or 

 less energetic, according to the quantity received by the surface 

 of the earth ; and this is regulated by the greater or less obliquity 

 of the latter to their direct or perpendicular influence ; or, in 

 other words, is in j)roportion to the square of the cosine of the 

 latitude, A calculation thus deduced would not be absolutely 

 correct for the purposes of cultivation ; but, it would certainly 

 form the surest basis relatively to which corrections could be 

 made; such as the diminution due to elevation, &c. The ratio 

 which the calculation would bear to the degrees of Fahrenheit's 

 thermometer should then be ascertained ; and, if it could be 

 corroborated by actual observations made by this instrument, 

 at every 10° of latitude, so much the better. For ultra-tropical 

 regions more especially, the table might usefully exhibit four 

 divisions: first, the temperature at the vernal equinox, which 

 would be found lower than the mean of the season, from the 

 earth still retaining in part the low temperature of winter ; 

 secondly, the temperature at the autumnal equinox, which would 

 be, for the contrary reason, as much warmer than the mean as 

 the vernal was colder ; thirdly and fourthly, the temperatures at 

 the summer and winter solstices. These tables might, also, be 

 exhibited on the margins of isothermal maps ; which, for greater 

 accuracy, might contain sections of the earth's surface included 

 by every 15° of longitude; and, if fifteen pages of the Gardener'' s 

 Magazine were so occupied, it would, I am convinced, form a 

 useful reference for the range of annual temperature ; and, to 

 make it still more complete, a table might be subjoined for that 

 of the diurnal temperattire, nearly which the plants of every 

 latitude naturally undergo. 



That, in regard to cultivation, we ought to " imitate nature," 

 is an expression universally assented to ; and, that we cannot 

 do so without some knowledge of her workings, cannot be 

 denied ; and the more correct that knowledge is, the more definite 

 will be the aim, and the greater the degree of perfection, of our 



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