Attraction on Clouds and Vapours. 63 



often increasing to a gale; the heaviest usually blows from 

 the north and north-west. These observations were made 

 between the 35th and tfi\i degree of north latitude, and 

 44° and 30° longitude west of Greenwich: the ship's 

 course being E. by N. 



There are certainly many places, in which a particular 

 wind almost invariably produces rain ; from the interven- 

 tion of a chain of hills, or even a single mountain that im- 

 pedes the regular course of the clouds, when moving in a 

 certain direction; and breaks them over the valleys below. 

 Or, the wind may be either sufficiently strong to over- 

 power the moon's attraction, or -so light as to afford no 

 assistance in spreading the clouds which have been col- 

 lected on or below the horizon, and thus produce an ef- 

 fect upon the weather contrary to what might have been 

 expected from the relative situation of the impelling powers ; 

 a circumstance which, though very material, did not 

 strike me when I began my observations ; and the ve- 

 locity of the wind is consequently unnoticed in the first 

 part of my journal. Our atmosphere may contain at times 

 so little vapour, as to be incapable of producing rain, al- 

 though the moon and wind were acting ever so much in 

 unison; but this can always be ascertained by the state of 

 the barometer. When also the moon's altitude or de- 

 pression is so great as to place her nearly in the zenith, or 

 the nadir, her attraction can of course avail but little, 

 either in assisting or counteracting the effect of the wind 

 from whatever point it may happen to blow: its power, in 

 short, must diminish in proportion as her distance from 

 the horizon increases. 



I do not pretend to improve, much less to controvert, the 

 theories of those many learned and scientific characters 

 who have written upon the nature and variation of the 

 atmosphere; for my knowledge in every branch of philo- 

 sophy is very slight; but I cannot help thinking, that a 

 little attention to the subject which I have noticed, would 

 frequently assist an observer of the weather, in foreseeing 

 with additional certainty an approaching change; and I 

 offer these remarks to the public, with no other view than 

 the possibility of their being investigated, by those who 

 possess the knowledge and leisure requisite in philosophical 

 studies, to the advancement of science, as well as the bene- 

 fit of those professions, in which a dependence is placed 

 upon the atmosphere. I remain, sir, 



Your respectful humble servant, 



Richmond Green, July 10,1810. JSALEM HARRIS. 



IX. On 



