Causes of certain Winds and Storms. 175 



Messrs Lewis and Clarke, at the mouth of the Columbia River, 

 had long continued gales from the south-west, and deluges of 

 rain. 



(h.) The violent winds that prevail at Cape Horn are not ac- 

 curately from the west point, but from some other between the 

 west and south. " I cannot, in any case, concur in recommend- 

 ing the running into the latitude of 61° or 62° before any endea- 

 vour is made to stand to the westward. We found neither the 

 current nor the storms, which the running so far to the south- 

 ward is supposed necessary to avoid ; and indeed, as the winds 

 almost constantly blow from that quarter, it is scarcely possible 

 to pursue the advice*."" 



(^■.) Cook's voyages into the high latitudes of the southern 

 hemisphere being made when the sun was in the neighbourhood 

 of the southern tropic, cannot be referred to as affording infor- 

 mation of unquestionable accuracy respecting the winds that 

 prevail in those seas. 



IV. Thunder-storms generally commence between mid-day and 

 sunset, and move from west to east, -f- 



(a.) Such persons as have paid any attention to the changes 

 of the weather in this country, must be well aware that our 

 thunder-storms begin in the after part of the day, and move from 

 west to east. They sometimes occur at night, but seldom after 

 midnight. The direction of their motion does not appear to de- 

 pend upon the predominance of the westerly over the easterly 

 winds, being much more constant and uniform than that predo- 

 minance ; but to be a result and a pi-oqfof a commotion excited 

 in the atmosphere at the time of tlieirjbrmation, and of a rush 

 of the air from the west towards the east, in consequence of some 

 new impulse just then communicated. 



(b.) The author of the article " Thunder," in the Encyclo- 

 paedia Perthensis, states, that along the eastern side of the island 

 of Great Britain, it is more frequent in the month of July than 

 at any other time of the year, which he attributes to the circum- 

 stance that a wind from the west then succeeds to the east wind 



" Cook, in Hawkesworth's Voyages, vol. ii. See also Clayton's account of 

 the Falkland Islands quoted above. 



+ In an easterly direction, not in the plane of the prime vertical. 



