1883 .] Analyst's of Books. 359 
the wind in storms. Taking the best instrument for the purpose, 
which is probably Robinson’s anemometer, now employed in this 
country, over the greater part of Europe, and in America, the 
question arises — Where is it to be fixed up ? We want a situa- 
tion where the wind is neither intercepted nor diverted from its 
even course. Everyone must have observed that when wind 
blows against a wall it rebounds in all directions, and rushes 
with a concentrated force round the end or over the top of the 
obstruction. It is observed by gardeners that these deflected 
currents are far more ruinous to vegetation than the direCt sweep 
of the wind in the open. It is at the corners of streets that 
umbrellas are turned inside out and that hats are whirled off into 
the realms of space. Hence the only spot at all suitable for 
ereding a wind-gauge is at the top of a pole, 20, 30, or perhaps 
40 feet high, set in the midst of an open field. We may add the 
further condition that this field should be in a level country. If 
on the slope of a hill, or amongst hills, the force of the wind 
may be either partially broken or intensified, according to its 
direction. 
There is a further consideration : we have no reason to sup- 
pose that the velocity of the wind in a tempest is uniform from 
minute to minute or from half-hour to half-hour. Even where 
there is no scope for interception, deflection, or rebounding, as 
on the open sea, we observe gusts of intensified violence inter- 
vening between lulls. Hence the average hourly velocity of the 
wind, however fairly measured, does not tell us what has been 
its maximum velocity. Now this maximum velocity is precisely 
what the engineer needs to know in order to adapt his structures 
to the greatest pressure which they may probably have to en- 
counter. This maximum velocity we are hitherto unable to find 
with anything like precision, and the highest authorites are here 
not at one. Our ignorance on this point was brought into full 
relief on occasion of the Tay Bridge disaster. As Mr. Laughton 
puts it, “ Engineers of the highest repute had no exaCt know- 
ledge as to whether the extreme probable force of wind should 
be taken as ten pounds on a square foot, or twenty, or forty.” 
In the tempest of October 14th, 1881, a pressure of 53 lbs. 
per square foot was indicated at Greenwich ; and at Liverpool, 
in March, 1871, a pressure of 90 lbs. is said to have been regis- 
tered. This result has been strongly questioned as far as England 
is concerned. But the speed of an American tornado is esti- 
mated as having a mean velocity of 392 miles per hour, and a 
maximum of 800 miles, which answers to a pressure of three- 
quarters of a ton per square foot. Such figures, to those who 
judge merely from the ordinary power of the wind, seem absurd. 
But if we examine the recorded effects of such tempests we find 
that the question takes a different aspeCt. In the tornadoes of 
the Western States heavy pieces of machinery have been carried 
away to considerable distances. In a West Indian hurricane 
heavy artillery has been dismounted and hurled away. 
