900 Marvels of the Universe 
west Wind is far more prevalent than any other ; the late Mr. Glaisher, of Greenwich Observatory, 
from the records of ten years’ observations, giving it an average prevalence (annually) of two thousand 
seven hundred and thirty-seven hours—more than twice that of any other. In Asia and Eastern 
North America the north-west Wind is perhaps more frequent. The Trade Winds (north-east or 
south-east, according to the hemisphere), blow regularly for many months at a time over wide areas ; 
the monsoons of the Indian Ocean blow for six months in one direction, and then again for the 
other six months of the year their 
direction is exactly reversed. Two 
main directions of air currents, 
due to the difference of tempera- 
ture between the equatorial and 
polar regions, are especially to be 
noticed, the equatorial warm 
currents northwards and south- 
wards towards either pole, and 
the polar cold currents from each 
pole towards the equator. It may 
here be noted that the Wind is 
named with reference to the points 
of the compass /vom which it 
comes, ¢.g., a south Wind is a Wind 
coming from the south and thus 
blowing towards the north. The 
intensity of the Wind is estimated 
in practice by experience of sen- 
sation, though various instruments, 
known aS anemometers, have 
been devised from time to time, 
but their indications are even yet 
not very reliable. According to 
its intensity, the Wind is variously 
estimated as light, moderate, 
fresh, strong, gale, storm or 
hurricane. A scale proposed by 
the late Admiral Beaufort, and 
consequently known by his name, 
is still in very general use amongst 
sailors and practical men gener- 
Photo by permission of ] [The One and All Association. 
A TORNADO IN OKLAHOMA, U.S.A. ally. On this a series of numbers 
A tornado is a mass of air in rapid rotation round a nearly vertical axis. from o to iF}, for a calm Ke to 
The cylinder of air, or ‘‘spout,’’ has a violent upward motion. The central 
REA nC oIGHIaD Cecones extol fecrnonm chidh dis, (NURIEAMNS,” IS walkem, Une Hommer 
telies Gino Lem Gf a weterepent. for cases when there is no Wind, the 
latter when its velocity is one hundred miles per hour or upwards, speeds not uncommon in tropical 
latitudes, but, fortunately, almost unknown in our too-much-maligned British climate. 
The name of cyclone, popularly applied to some violent but comparatively rarer storms of the 
tropics, is given by meteorologists to regions of atmospheric circulation, usually more or less circular 
or oval in form (whence the name—xéxAoe, Greek=circle), in which the air moves round and 
inwards towards a central region of comparatively lower pressure, and the main difference between 
the various kinds of disturbances of this nature is a difference in size and sometimes in shape. 
