508 Meteorology. 
summer than winter, and in warm countries 
than in cold. ) tae 
We may now enquire into the cause why 
less rain falls in the first six months of the 
year than in the last six months. The whole 
quantity of water in the atmosphere in J anu- 
ary, is usually about 3 inches, as appears 
from the dew point, which is then about 82°. 
Now, the force: of vapour at that, tempera- 
ture is .2 of an inch of mercury, which is 
equal to 2:8 or 3 inches of water. ‘The dew 
point in July, is usually about 58 or 59°, 
corresponding to .5 of an inch of mercury, 
which is equal to 7 inches of water; the 
difference is 4 inches of water, . which the 
atmosphere then. contains more than | in the 
former, month. Hence, supposing the usual 
intermixture ,of; currents of air in both the 
inter ‘vening periods to, | be the: ‘same, the rain 
ought,to. be 4 inches less in the former period 
of the, year than the average, and: 4 inches 
more in the latter period, making a difference 
of 8 inches between the two periods, which 
nearly accords with the ‘preceding obser- 
yations. 
In the preceding estimations of the while 
quantity, of water in the incumbent atmos- 
phere of any place, I take for granted, that 
an.atmosphere of steam is blended witht the 
