CLIMATE. 



CLIMATE. 



under the observation of an enlightened popu- 

 lation ; they are advancing with astonishing 

 rapidity ; and they ought, in some degree, sud- 

 denly to produce the meteorological alterations 

 which many ages have scarcely rendered ap- 

 parent in our old continent. This country is 

 North America. Let us see, then, how clear- 

 ing the country affects the climate there. The 

 may evidently be applied to the ancient 

 condition of our own countries, and we shall 

 find that we may thus dispense with a priori 

 considerations which, in a subject so compli- 

 cated, \\-onld probably have misled us." 



There is great force in the following remarks 

 of Dr. Forry, and the facts adduced in their 

 support: 



" Dense forests and all growing vegetables 

 doubtless tend considerably to diminish the 

 temperature of summer, by affording evapora- 

 tion from the surface of their leaves, and pre- 

 venting the calorific rays from reaching the 

 ground. It is a fact equally well known that 

 snow lies longer in forests than on plains, be- 

 in the former locality, it is less exposed 

 to the action of the sun; and hence, the win- 

 ters, in former years, may have been longer 

 and more uniform. As the clearing away of 

 the forest causes the waters to evaporate and 

 the soil to become dry, some increase in the 

 mean summer temperature, diametrically con- 

 trary to the opinion of Jefferson and others, 

 necessarily follows. It is remarked by Um- 

 freville that, at Hudson's Bay, the ground in 

 open places thaws to the depth of four feet, and 

 in the woods to the depth only of two. More- 

 over, it has been determined by thermometrical 

 experiments that the temperature of the forest, 

 at the depth of twelve inches below the surface 

 of the earth, is, compared with an adjacent 

 open field, at least 10 lower, during the sum- 

 mer months ; whilst no difference is observable 

 during the season of winter. 



" It may, therefore, be assumed, that although 

 cultivation of the soil may not be productive 

 of a sensible change in the mean annual tem- 

 perature, yet such a modification in the distri- 

 bution of heat among the seasons may be 

 induced as will greatly influence vegetation." 



Bearing upon this point, Dr. Fony furnishes 

 a table exhibiting a comparative view of the 

 atmospheric temperature at Philadelphia, at 

 intervals of about a quarter of a century, (from 

 1771 to 1S21,) which shows a successive de- 

 crease in the mean of winter, and an increase in 

 the means of spring, summer, autumn, and 

 whole year. Some allowance must be made in 

 these estimates for the effects of increase in the 

 size of the city, and the additional shelter in 

 winter, and opportunity of accumulating heat 

 in summer thus afforded. All, towns are ob- 

 served to irrow warmer as they extend their 

 limits. When, therefore, we find a decline in 

 the mean temperature of winter, notwithstand- 

 ing the extension of the city limits, we must 

 infer that it can arise from no other cause than 

 a general diminution in the winter temperature 

 throughout the country. 



Any changes in the climate of the United 

 States as yet perceived, are very far from 

 justifying the sanguine calculations indulged 

 in a few years ago by a writer on the climate 



and vegetation of the fortieth degree of North 

 latitude, who, in concluding his essay, says: 



'But there will doubtless be an amelioration 

 in this particular," (severity of cold,) " when. 

 Canada and the United States shall become 

 thickly peopled and generally cultivated. In 

 this latitude, then, like the same parallels in 

 Europe at present, snow and ice will become 

 rare phenomena, and the orange, the olive, 

 and other vegetables of the same class, now 

 strangers to the soil, will become objects of the 

 labour and solicitude of the agriculturist." 



Had this writer extended his inquiries a 

 little further, he might have found that the 

 region of Oregon, lying west of the Rocky 

 Mountains, though as yet in a primitive state 

 of nature, has a climate even milder than that 

 of highly cultivated Europe in similar lati- 

 tudes. And again, China, situated precisely 

 under the same conditions as the United States 

 in regard to the sea, though long since sub- 

 jected to the highest state of agricultural im- 

 provement, possesses a winter climate as 

 rigorous, and some assert even more so, than 

 that of tlit- United States in similar latitudes. 

 See table of mean temperature under the head 

 A TMnm-imiK, pacre 126. 



CLIMATE. INFLUENCE OF, ON THE 

 FRUITFULNESS OF PLANTS. The fol- 

 lowing observations upon a topic 6f natural 

 history of great interest to the agriculturist, 

 are quoted from the same sensible and elo- 

 quent American writer, to whom reference has 

 been made under the head of the ACCLIMATING 

 PIMM IPLE OF PLANTS. 



"The cultivated plants yield the greatest 

 products near the northernmost limit in which 

 they will grow. 



" I have been forcibly impressed with this fact, 

 from observing the productions of the various 

 plants, which are cultivated for food and cloth- 

 ing in the United States. The following instances 

 will go far to establish the principle, viz.: 



"The cotton, which is a tropical plant, yields 

 the best staple and surest product in the tem- 

 perate latitudes. The southern parts of the 

 United States have taken the cotton market 

 from the East and West Indies, both as regards 

 quantity and quality. This is partly owing to 

 the prevalence of insects within the tropics, 

 but principally to the forcing nature of a verti- 

 cal sun. Such a degree of heat developes the 

 plant too rapidly runs it into wood and foli- 

 age, which become injuriously luxuriant; the 

 consequence is, there are but few seed pods, 

 and these covered with a thin harsh coat of 

 wool. The cotton wool, like the fur of animals, 

 is, perhaps, designed for protection ; and will 

 be thick and fine in proportion as the climate 

 is warm or cool. Another reason is to be 

 found in the providence of the Deity, who aims 

 to preserve races rather than individuals, and 

 multiplies the seeds and eyes of plants, exactly 

 as there is danger of their being destroyed by 

 the severity of the climate, or other causes. 

 When, therefore, the cares and labours of man 

 counteract the destructive tendency of the cli- 

 mate and guaranty their preservation, they 

 are, of course, more available and abundant. 



"The lint plants, flax, hemp, &c., are culti- 

 vated through a great extent of latitude , but 



335 



