272 
THEORY OF HAl.N. 
Fahr. to raise it in vapour, and that we have most rain when the air 
is at 50 degs.” I answer, that the first part of the assertion has no 
foundation, as water will evaporate at a heat of less than 40 degs. 
and that for the second part to help his argument, we must suppose, 
for example, the evaporation of the water, and the recondensation of 
the vapour, to happen at the same time : hut the vapour of water 
being lighter than atmospheric air, in the proportion of ten to 
fourteen, will ascend to the higher regions of the atmosphere, and 
and through it will be there condensed, it is not by a sudden change, 
but first passing into the state of small hollow globules, still con¬ 
taining vapour, in which form it is called vesicular vapour, this forms 
the clouds, which, being of the same specific gravity as the air, float 
about in it, but being gradually condensed, descend in proportion, 
and finally fall in the shape of rain. 
To his second objection, viz. “ that when we have the greatest 
heat, as in summer, we have the least rain,’’ I answer that though in 
winter we have the most rainy days, yet in summer, and the warm 
parts of autumn and spring, we have the greatest quantity of rain. 
His third objection, viz, “ that the vapour from the water, on 
rising to the height of 100 yards, would be condensed and immedi¬ 
ately fall, like the water from the refrigeratory of an alembic,” I have 
answered in my first paragraph, and the simile seems to me not to 
help his cause, as all the vapour from an alembic is not condensed, 
unless an artificial degree of cold is applied, that is only to be found 
in the highest regions of the atmosphere. 
His fourth argument, “ that we have the most rain at nights, and 
in winter,” tells against him, for it is natural that a cold night should 
condense the vapour raised by the heat of the day, and the presence 
of the sun’s rays is not at all necessary to raise this vapour, the 
mere warmth of the air being sufficient, witness the evaporation of 
water in a cold room. 
In these first objections, especially in the second, he has allowed, 
nay partially founded his arguments, on the fact of water being 
raised in vapour by the sun ; but in tbe next he denies this fact, on 
the strength of a glass not being moistened when held over a river; 
certainly it will not, while the air remains sufficiently hot, not to 
condense the vapour, but when the air cools, by the absence of the 
sun, the vapour will be condensed on the glass and will be visible in 
the air, on account of such condensation. 
As to the sixth argument, “ that there always should be most rain 
in tropical climates, were the old theory true,” I say, that it is not 
necessary that the vapour raised in one part of the earth, should al- 
