l04 ■ PHILOSOPHICAL TRANSACTIONS. [aNNO 1085. 



wise, a greater degree of lightness than the other parts, those lightened parts 

 ascending, and the heavier subsiding ; as when water, beer, or other thin fluids 

 are gradually heated by a fire underneath ; the lower parts being first warmed, 

 ascending to the top, while the colder and heavier subside ; whence we find in 

 such cases, that bubbles arise, and the liquor at the top is warmer than that at 

 the bottom. But in case what is warmed be of a thicker consistence, so 

 that the parts cannot readily shift places, that at the bottom will be hotter. 



From such considerations as these. Dr. Garden well observes, that some 

 parts of the air being thus, by rarefaction, or increasing its spring, or other- 

 wise, become lighter than others; these heavier parts rushing into the places of 

 those lighter, may cause a wind as from such parts. And this 1 take to be very 

 true, though such accidents happening very variously and uncertainly, will cause 

 such confusion of motions, and disturbance of each other, that it will be hard 

 to reduce them to a regular adjustment. But I add thereto, that the earth's 

 diurnal motion, compounded with its annual, the one in some parts accele- 

 rating, in others retarding the other ; and its difference in difl^erent times of the 

 year, by reason of the obliquity of the zodiac to the equinoctial, and in differ- 

 ent times of the month, because of the moon's different position, which is an 

 appendance to the earth's motion, and thereby differently affects it, and accord- 

 ing to the different place of the earth and moon, as to the aphelion or perihelion 

 of the one, and the apogasum or perigaeum of the other, seem to me greatly 

 to influence, not only the tides, but the winds also ; especially the breezes 

 and trade-winds, which at certain times of the day or month, or of the year, 

 are observed to blow constantly, or most frequently, from a particular point. 

 And I am not sure that the body of earth and water, or terraqueous globe, is 

 exactly spherical, allowing only for the small inequalities of hills and dales^ 

 which in a body of that magnitude are inconsiderable, but may have somewhat 

 of an oblong spheroid, having a longer axis from pole to pole, then at the 

 equator. And though this cannot be much, because of the earth's shadow in 

 the moon's eclipse appearing circular, and the descent of heavy bodies being 

 always, as to sense in a perpendicular to the horizon ; yet, if it be but little, 

 this, with the. compound motions before-mentioned, will give the air a con- 

 siderable disturbance. To which I may add also, that we are not sure that the 

 seas and continents are so adequately adjusted to each other, as that its centre 

 of gravity coincides with its centre of magnitude, by which the confusions of 

 the air's motions would be yet greater. 



From the comparative weight or lightness of the air at different times. Dr. 

 Garden deduces also the rising or falling of vapours in it ; and this is certainly to 

 be admitted also. Only I add, that these static principles chiefly take place. 



