22 



NATURAL HISTORY OF VERMONT. 



Part I. 



CHANGE OF CLIMATE. 



CCRRENTS OF THE OCEAN' 



winds to be descending currents from the 

 hiorher regions of the atmosphere ; and 

 hence their cohlness. Docl. liolyoke at- 

 tributed the coldness of onr climate to the 

 extensive forests of evergreens. Doct. 

 Williams, the able historian of Vermont, 

 attributed it to the forest state of the 

 country, and has endeavoured to prove 

 that, eighteen centuries ago, the climate 

 of Europe was even colder than that of 

 America at the present time.* But other 

 writers liave, with equal plausibility, 

 shown that no considerable change has 

 taken place in the mean temperature of 

 Europe within tliat period. f The fact, 

 moreover, that the^ western coasts of 

 America, which are wholly uncultivated, 

 are very much warmer than the eastern 

 coasts of Asia in the same latitude, which 

 are cultivated to considerable extent 

 shows that these differences of tempera- 

 ture do not depend upon cultivation, nor, 

 indeed, upon any of the causes which 

 have been mentioned, but upon some more 

 general cause. And this cause, we be- 

 lieve, is to be sought in the influence of 

 the ocean upon the prevailing winds in 

 high northern latitudes. We regard the 

 ocean as the great equalizer of temi)era- 

 ture upon the surface of our globe — as the 

 instrument for distributing the heat of 

 the equatorial regions towards the poles 

 and bringing tlience cold towards the 

 equator, and thus meliorating the climate 

 of both. We look upon it as a truth es- 

 tablished both by theory and fact that 

 there is a general circulation of the wa- 

 ters of the ocean between the equatorial 

 and polar regions — that the warm water 

 from the equator is flowingalong the sur- 

 face of the ocean towards the poles, while 

 the colder water from the poles is ad- 

 vancing along the bottom of the ocean to- 

 wards the equator. Such a motion of the 

 waters might be inferred, as the result of 

 the unequal distribution of heat through 

 the oceanic mass, increased by the rota- 

 tion of the earth on its axis. But inde- 

 pendent of this, facts furnish indubitable 

 proof of its existence. The temperature 

 of the earth, at a distance below the sur- 

 face, being a pretty correct index of the 

 mean temperature of the climate, with- 

 out the circulation we have supposed, the 

 temperature of the ocean at consider- 

 able depths, ought, particularly in the 

 warmer parts of the year, to be as 

 high, at least, as the mean annual tem- 

 perature. But on the contrary, observa- 

 tion proves it to be much lower. In lati- 

 tude 6~°, where the mean temperature is 

 39°, Lord JVIulgrave found, on the 20th 



♦William-;' fiistory of Vermont, Vol 1, p. 475. 

 ^ Edinburgh Review, Vol. XXX, p. 25. 



of June, when the temperature of the air 

 was 46^°, that the temperature of the 

 ocean at the depth of 46rf0 feet, was 26", 

 or 6° bellow the freezing point. On the 

 31st of August, in latitude 6'.1° where the 

 annual temi)erature is 38'', that of the air 

 being o'.l.^", the temperature of the water 

 at the depth of 4038 feet was 32°.* At 

 the tropic where the temperature does 

 not vary more than 7° or 8° during the 

 year, at the depth of 3600 feet the tem- 

 perature of the water was found to be on- 

 ly 53°, while that of tlie air was 84°, 

 making a ditferenco of 31°, and indicating 

 a degree of cold in the lower parts of the 

 ocean nearly 23° niore intense than is ever 

 experienced in the atmosphere in that 

 latitude, t How else can we account for the 

 coldness of these waters, but by suppos- 

 ing them to come from liigher latitudes in 

 the mann(>r we have described .'' 



Of the opposite motion of the warmer 

 waters along the surface of the Atlantic 

 ocean, from the eqtiatorial towards the 

 polar regions, the gulf stream, the currents 

 setting along the western coasts of Nor- 

 way, and the vast quantities of tropical 

 productions, lodged upon the costs and 

 islands of the northern ocean, afford a- 

 bundant jiroof. 



Now tiiis transportation of the colder 

 waters towards the equator and of the 

 warmer waters towards the poles, serves, 

 as already remarked, to mitigate the other- 

 wise intolerable heat of the former, and 

 the excessive cold of the latter; and af- 

 fords an obvious manifestation of the wis- 

 dom and goodness of providence. And 

 it is to the influence of the warm superfi- 

 cial waters of the ocean, which have 

 come from tropical regions, upon the 

 winds, or currents of the atmosphere, that 

 we are to look for the cause of the difl'er- 

 ence of temperature in the climate of the 

 eastern coasts of North America and the 

 western coasts of Europe, and also in that 

 of the eastern coasts of Asia and the west- 

 ern coasts of North America. If we ob- 

 serve the gulf stream, which is only a 

 concentration by the tjade winds of those 

 warm waters which are flowing norther- 

 ly along the surface of the ocean, we 

 shall perceive it to be very narrow, pre- 

 senting to the atmosphere only a small 

 surface of its warm water, vvhile near the 

 American coast. But as it proceeds to 

 the northeast its warm waters are spread 

 out upon the surface of the ocean and are 

 thrown directly along or upon the west- 

 ern coasts of Europe. Observation also 

 shows that the prevailing winds in high 

 northern latitudes, are from a north west- 



* Count Runiford's Essays, Vol. II. page 304. 

 t Phil. Transactions, 1752. 



