98 Richard Adie on Currents of Wind. 
The action of undulating ground in checking currents of air 
refers to localities within a certain range of their influence ; 
in such situations trees are found in a more luxuriant state 
of growth near the sea, than would have been the case if the 
ground around them had been flat; at the same time the 
fact must not be lost sight of, that while hills protect much of — 
the surface from winds, they also expose certain localities 
where the wild winds roar more than on any sea-girt plain. 
A calculation of the weight of air which a ridge of very 
moderate elevation will raise hourly, may startle some of 
your readers. Take a ridge of 10 feet high on a sea-board 
of 100 miles in length. According to Mr Hartnup, in his 
meteorological results for the Liverpool observatory, 1852, the 
mean horizontal motion of the air for the year is 13 miles 
per hour. The mean weight of the air that crosses may be 
counted at 2 lb. per cubic yard, which is nearly 303 grains 
to the 100 cubic inches. And suppose that the stratum of 
the mass in motion is 300 feet thick, the calculation founded 
on these data shews the weight of air raised 10 feet during 
every hour, to be 310 millions of tons. In the mean state of 
dryness, the atmosphere contains 14 parts per 1000 of 
aqueous vapour, which proportion gives for the water raised 
10 feet along a sea-board of 100 miles, 44 millions of tons 
per hour—a large quantity of this vast weight being capable 
of condensation into rain. 
The gales required to form the ‘ spoon drift’? which I © 
have described as so destructive to vegetation, may be judged 
of from the subjoined notice, extracted from Mr Hartnup’s 
report. 
The following results shew the comparative violence of 
the four heaviest gales of wind which passed over the, ob- 
servatory during the year 1852 :— 
Greatest velocity of the 
Extreme pressure air between any one 
on the square foot. hour and the next hour 
following. 
January 4. 28 pounds : 53 miles. 
tire 9. 2B vet ; ; 62 
December 25, 42... ; 70 
27. Df are F : ya 
