METEOROLOGY AND CLIMATOLOGY. 
33 
NORTHERN 
HEMISPHERE 
well-known danger to sailing ships caught in such a storm at sea, 
because there is no wind to move the vessel, but a tremendous sea driven 
in from the gale which rages all round from every point of the compass. 
The law of storms has been very fully 
studied, and rules have been drawn up to 
enable sailors to ascertain the direction in 
which the centre of an approaching cyclone 
lies and the direction in which it is moving. 
In a work intended mainly for travellers 
on land it is not necessary to give these 
rules; all that is required is to tell how 
the approach of dangerous storms may be 
.ascertained some time in advance. 
The fact that the barometer is high or 
low is in itself of no value for prediction. 
Tim important thing to know is the dis¬ 
tribution of atmospheric pressure at a 
; given moment over a considerable area. 
To the isolated observer this is impossible, 
and he can only judge of the state of the 
atmosphere by observing the rate at which 
the barometer is falling or rising. Thus, 
if for several days the barometer has been 
steadily and slowly rising, he will probably 
be right in believing that an anticyclonic 
condition is establishing itself, and that 
the weather may be expected to continue 
line for many days to come, even after a 
gradual fall of the barometer begins. A 
sudden fall of the barometer, on the other 
hand, is always a sign of wind, and usually 
of wet weather as well. This is a particu¬ 
larly valuable sign of approaching storm 
in those parts of the world where, as in the tropics, the normal weather 
is very uniform and steady. In such places a very sudden fall, say one- 
tenth of an inch in an hour, is a sure precursor of a violent storm. As 
the barometer continues to fall, the wind will probably continue to 
VOL. II. d 
SOUTHERN 
HEMISPHERE 
Fig. 9. Cyclone Paths and 
Circulation of Winds in Cy¬ 
clones in the Northern and 
Southern Hemispheres. 
