CYCLONES. 153 
of the earth there is exactly half the distance that it is round the 
equator. Being only half this distance, it follows, then, that 
anything apparently at rest on latitude 60° is really moving at half 
the rate that anything on the equator is moving, that is to say, it 
is moving round at the rate of 518 miles an hour instead of 1,036 
miles. The earth rotates from the west towards the east, as you 
know ; suppose, therefore, something, say a mass of air, which is 
travelling at the equator at the rate of 1,036 miles an hour towards 
the east, to be suddenly tranferred to latitude 60°, still having its 
original motion, it would there travel ¢zce as fast to the east as 
the earth is moving ; consequently, to anyone standing on the 
earth there the motion of the air would be felt as a terrific wind 
blowing from west to east, at the rate of 518 miles an hour ; that is 
to say, it would be blowing with a force far exceeding the greatest 
hurricane that ever blew. Now, of course, it is impossible to 
transfer anything from the equator to latitude 60° in the way I 
have supposed ; but from this exaggerated case I wished to show 
you, as clearly as I could, that anything, even being slowly moved 
from the equator towards the north pole, must be inclined to 
take a direction towards the east, owing to the fact that it is 
always leaving a portion of the earth’s surface, which is moving 
faster, for a portion that is moving slower. Every step taken 
from the equator towards the north pole must take one to a more 
slowly moving spot. Now it follows, from what I have said, that 
any wind starting in the northern hemisphere to blow from the 
south towards the north mzs¢ gradually change its course towards 
the east, that is to say, a south wind mus¢ become a south-westerly 
wind. (By ‘‘south westerly wind” here is meant any wind near 
that point, not of necessity a wind due south-west.) We have so 
far only spoken of movement on the earth from the south north- 
wards ; now let us consider the reverse movement, ze, from 
north to south. It will be readily seen now that we have move- 
ment from a more s/ow/y rotating portion of the earth to a guicher 
one. In this case, therefore, the change in the course of the 
_ wind will be reversed. A north wind starting to blow south will 
have, as it were, the earth running against it, thus converting a 
