Proximate Causes of certain Winds and Storms. 283 



ics is more immediately derived from the simplest and clearest prin- 

 ciples, than that there must be a descending and ascending current, 

 moving with the same rapidity at its extremities. These vertical 

 currents are not to be regarded as effects, but causes, of the horizon- 

 tal one. They are first in the order of causation, and the horizontal 

 current could not exist without them. 



No notice is taken here of the anomalies with which this depart- 

 ment of nature abounds, beyond every other. Causes analogous to 

 those which produce thunderstorms from the western quarter, and in 

 the after part of the day, in most countries, will bring them on at 

 other hours, and from other points of the compass, at particular times 

 and in particular places. It is suggested, however, that conclusions, 

 drawn immediately from the first principles of the equilibrium and 

 movement of elastic fluids, and whose accuracy is rendered proba- 

 ble by their explaining a great number of phenomena, are not to be 

 regarded in the light of a mere hypothesis- 



Of the Peculiarities of the Climate ofJYorth America. 



The climate of North America, or rather of that part of it lying 

 east of the Rocky Mountains, when compared with that of Europe 

 under the same parallels, is found to differ from it remarkably in two 

 particulars. 



1. The mean temperature is several degrees lower. 



2. The vicissitudes of temperature are much greater. 



The first setders of North America found that they experienced 

 a cold in winter much more severe than they had been accustomed to 

 in their native country, and drew the inference that the western con- 

 tinent is much colder on the same parallels, than the eastern. But 

 they found also that the American is hotter than the European sum- 

 mer ; and as there had been no accurate observations for determin- 

 ing the mean temperature, philosophers ventured on the adoption of 

 the opinion that it is much the same on both sides of the Ariantic, 

 and that the two continents differ onl}^ in the extent and suddenness 

 of the vicissitudes to which they are liable. This opinion is still en- 

 tertained and defended by Mr. Leslie. 



" The extremes of summer and winter probably differ more in 

 America than in the old continent ; but the mere (mean ?) tempera- 

 ture on every parallel appears, when carefully taken, to be nearly 

 the same."* 



* Supp. to Encyclopedia Britlanica, Art. Climate. 



