428 PHILOSOPHICAL TRANSACTIONS. [aNNO I69O-I. 



vapour from the surface of the sea in a day's time, which was so far approved 

 by some honourable members of this society, that I have received their com- 

 mands to prosecute those inquiries, and particularly in relation to the method 

 used by nature to return the said vapours again into the sea ; which is so justly 

 performed, that in many hundreds of years we are sufficiently assured that the 

 sea has not sensibly decreased by the loss in vapour, nor yet abounded by the 

 immense quantity of fresh water it receives continually from the rivers. To 

 demonstrate this equilibrium of receipt and expence in the whole sea, is a task, 

 too hard for me to undertake, yet in obedience to those whom I have the ho- 

 nour to serve I shall here offer, what to me has hitherto seemed the most satis- 

 factory account of this grand phenomenon. I have formerly attempted to ex- 

 plain the manner of the rising of vapour by warmth, by showing that if an atom 

 of water were expanded into a shell or bubble, so as to be ten times as large in 

 diameter as when it was water, such an atom would become specifically lighter 

 than air, and rise as long as that flatus, or warm spirit, that first separated it 

 from the mass of water, shall continue to distend it to the same degree; but 

 that warmth decreasing, and the air growing cooler, and so specifically lighter, 

 the vapours consequently will stop at a certain region of the air, or else de- 

 scend ; which may happen on several accounts, as will appear below. Yet I 

 assert not that this is the only principle of the rise of vapours, and that there 

 may not be a certain kind of matter whose conatus may be contrary to that of 

 gravity ; as is evident in vegetation, wherein the tendency of the sprouts is 

 directly upwards, or against the perpendicular. But whatever be the true 

 cause, it is in fact certain that warmth does separate the particles of water, and 

 emit them with a greater velocity as the heat is more intense, as is evident in the 

 steam of a boiling cauldron, wherein likewise the velocity of the ascent of the 

 vapours visibly decreases till they disappear, being dispersed into and assimilated 

 with the ambient air. Vapours being thus raised by warmth, let us in the 

 first place suppose, that the whole surface of the globe were all water to a great 

 deptii, or rather, that the whole body of the earth were water, and that the sun 

 had its diurnal course about it. It would follow, that the air of itself would im- 

 bibe a certain quantity of aqueous vapours, and retain them like salts dis- 

 solved in water ; that the sun warming the air, and raising more plentiful va- 

 pours from the water in the day time, the air would sustain a greater proportion 

 of them, as warm water will hold more dissolved salts, which, upon the absence 

 of the sun in the nights would be all again discharged in dews, analogous to 

 the precipitation of salts on the cooling of the liquors, nor is it to be thought 

 that in such case there would be any diversity of weather, other than periodi- 

 cally, every year alike ; the mixture of all terrestrial, saline, heterogeneous 



