Trade- Winds, Eio Janeiro. &c. 111 



arrival at 30° N. ; after which, she for the most part had per- 

 manentlvjthoughnot in exact succession, the N.E. j N. N.E. by 

 N., &c. trade-winds as far as 37" 46' N.; where, on the 26th of 

 June, at 1 1 A.M. in 44" 00' west longitude, not very remote from 

 the Great Bank, she fell in with a moderate breeze from the S.E. 

 by E., that freshened and veered more to the southward towards 

 night. It is likewise known, that at any intermediate parallel 

 between these principal parallels of limitation and the equator, 

 the wind corresponds, under the intervening differences just 

 stated, to some intermediate point between either of these points 

 and the east. Hence, it is evident, that there is an east wind at 

 the equator, or at some intermediate ])arallel, where the heat is 

 most intense. As the equator is the centre of the sun's declina- 

 tions, and as the sun is on it twice in the year, and on each of 

 the tropics but once, it is obvious that the equatorial parts ought 

 to be the hottest ; but from the difference of densities between 

 the two hemispheres, and from the sun's being about eight days 

 longer in the northern than in the southern hemisphere (besides 

 other reasons, which 1 shall presently assign), the parallel might 

 be reasonably presumed to be on the northern side; and accord- 

 ingly it is found, from repeated observations, to be between the 

 2d and 5th or 6th degree of north latitude. On our way out to 

 Rio Janeiro, I found the temperature between those latitudes 

 higher than that between the same latitudes south, notwith- 

 standing the greater obliquity of the sun's rays at the same time. 

 At the north side of the equator, as far as 7° or 8°, the winds 

 thus counteract each other, and are productive of calms, or light 

 breezes that are continually shifting ; a circumstance rarely re- 

 marked in cprresponding latitudes south. 



It will, I trust, not be superfluous here to extend the forego- 

 ing comparison concerning the difference of temperature beyond 

 the tropical circles. It appears from Cook's tracks in the southern 

 hemisphere, that the polar ice there extends further beyond the 

 antarctic circle, than what the north polar ice does beyond the 

 arctic circle. Independently, however, of local circumstances, it 

 also appears, that the detiree of temperature arising from equal 

 declinations of the sun is in general lower in the same parallels 

 south than north. This, considered chiefly in a scieniitic and 

 partly in a hypotiietical light, may be accounted for, briefly, as 

 follows : 



1. We know from the relative positions of the earth in the 

 ecliptic, that the sun is more remote during the soutliern winter, 

 by about three millions of miles, et cceteris paribus, than it is du- 

 ring the northern winter, et vice versa. Hence the diminution of 

 the sun's influence, as it relates to the southern hemisphere, is 

 not only increased in proportion to the increasingobliquity of his 



rays, 



