Jtmospherical Phenomena. 25S 



rection for sever^ days in succession. When, however, we 

 examine carefully the directions of the wind, we not unfre- 

 quently find a tolerably regular order in which they alternate. 

 Thus, when the north wind blows at a place, after some time 

 it veers to the north-east, afterwards to the east, and in this 

 order goes through all points of the compass, until it returns 

 again to the north. The time occupied by such a circumvolu- 

 tion amounts to a smaller or greater number of days. Although 

 the wind often changes suddenly, from one point of the com- 

 pass to another, and passes through several points in an order 

 just the opposite of that given above, yet observations made in a 

 multitude of places go to shew that the first mentioned is the 

 more usual sequence. Francis Bacon (Lord Verulam) in his 

 trektise on winds, brought forward this remark of sailors, and 

 in later times, navigators have often spoken of it in their nar- 

 ratives without natural philosophers assigning it much im- 

 portance, until recently Professor Dove has proved the belief 

 to be founded in fact, by the aid of many arguments and ob- 

 servations collected from various quarters of the globe ; and 

 although I do not agree with all the assertions of this acute 

 and talented natural philosopher, yet I regard the leading fea- 

 ture of his investigation as perfectly well founded. 



Explanation of the variable Winds, — If we examine with 

 more care the circumstances attending the winds in higher 

 latitudes, we ought, in our hemisphere, according to the theory, 

 to find there, as at the equator, a north-east wind, since 

 the regions lying more to the north are also colder. This 

 prevailing north-east wind is, however, interfered with by 

 the already mentioned descending south-west wind, which at 

 the same time serves, by means of the movement in the upper 

 strata, in countries lying to the north, to replace the air which 

 has been moved near the surface towards the equator. Thus 

 the theory of the trade-winds developed by Halley, requires 

 in our regions two diametrically opposed winds, which, for the 

 sake of brevity, we shall designate N£. and SW. Expe- 

 rience perfectly confirms this, for almost in every part of 

 Europe of which we possess meteorological observations kept 

 for several years, the winds from these quarters are the most 

 frequent ; but, at the same time, we perceive that the south- 

 west is more frequent than the north-east, wherever there are 

 no mountains or similar causes to produce a derangement. 



