( 10 .) 
There is another Opinion concernfng the Rife of 
Vapours, namely, that^ tho* Water be Ipecifically 
heavier than Air, yet if its Surface be encreafed by 
very much diminilhing the Bulk of its Particles, 
when once raifed, it cannot cafily fall ^ becaule the 
Weight of each Particle dimini flies as the Cube Root 
of its Diameter, and the Surface to which the Air 
refills, only as the Square Root of the faid Diame- 
ter : That we fee this in the Dull in Summer, and 
' in Menftruums that fuftain Metals dillblved, which 
are Ipecifically heavier than the Menftruums. 
But this will not explain the Thanomenon ; be- 
caule though the Encreafe of Surface (the Weight 
remaining the lame ) will in a great Meafure hinder 
( or rather" retard') the Defcent of fmall Bodies 
moving in the Air, by reafon of its great Refiftance 
to fo large a Surface ; it will for the lame Reafon 
alfo hinder the Afccnt. For the Rile of Dull is owing 
fo the Motion of Animals Feet in it, or to the Wind : 
Whereas Vapours rife in calm Weather, as well as 
windy ; neither do they, like the Dull, always fall 
to the Ground when the Wind ceafes to blow. 
The third Opinion, and which is moll commonly 
received, is, that by the A^ion of the Sun on the 
Water, fmall Particles of Water are formed into hol- 
low Spherules filled with an Aura, or finer Air 
highly rarefied, fo as to become Ipecifically lighter 
than common Air, and confequently that they mull 
rifo in it by hydroftatical Laws. As for Example, 
If a Particle of Water, as it becomes a hollow 
Sphere, be only encreafod ten Times in Diameter, 
its Bulk will be encreafed a thoufand Times ; there- 
I . ' fore 
