44 Dr. Ballot on the importance of Deviations^/w^ the mean 



impart warmth to the surrounding parts : it will readily be per- 

 ceived that these values must ever be the same for each place 

 situated in the same latitude and elevation above the sea. On 

 what does it depend that MTz/ and intfare not found alike in 

 all the places in the same parallel, but always different in every 

 different place; lower in this, higher in that, than ®j/ and 

 0/? If there was a parallel circle which extended wholly over 

 a continent, or if we passed regularly over a parallel circle in 

 a ship, and if we determined the MTz/ in n different selected 



2 MTy 



places, then would be nearly expressed by ©j/ ; the 



?i 



value so obtained would, however, be somewhat greater than 

 %y, because there is more air drawing towards the north than 

 towards the south over a whole parallel circle, that southern 

 air at the same time being warmer ; and also because, near 

 the equator, the latent heat which is employed in the vapori- 

 zing of water is greater than that which is freed by rain ; and, 

 on the contrary, in higher latitudes there is more freed than 

 expended on the formation of vapour. This is also a cause 

 why on the land ©j/ must be something less than at sea. If 

 we would nicely calculate this influence, we ought equally to 

 distinguish between rain that is formed in different altitudes. 

 Properly we ought to infer theoretically (eh/, and equally so 

 Of, from the warmth which emanates from the sun to us every 

 day; from the warmth which every day and night issues from 

 beneath the surface of earth ; and from the warmth that is 

 produced by animals, consumed by plants, lost by radiation, 

 given by condensation of vapour. The difference between Sy 

 so obtained, and MTy, (MTy— ®j/), at a certain place, is to be 

 ascribed to the influence of the wind during the year; simi- 

 larly, mtf—$f is the influence of the wind which prevails in 

 February at that place. How far we are as yet from such a 

 determination may be seen, for example, from the meteorology 

 of the late illustrious Daniell. But even if it could be ob- 

 tained, it would, however, not be fit for a great space of time; 

 for certain it is, that the resultant of the winds of a whole year 

 would not have the same influence on the temperature as the 

 different components. This will appear more evident to any 

 one who directs his attention to the differences mty—Qy, 

 mtf—$f, mtjl—Sjl, &c. He would find, not only for every 

 place, but also for every month of the year, different influences 

 for the same wind ; the same wind producing a different cool- 

 ing or heating power in different seasons, a circumstance of 

 which account is not taken in computing the resultant. 



Art. II. We will suppose that not only S and 0, but also MT 

 and mt were obtained at a certain place from a long series of 



