, 1877-07-28

49, ~ 'NA 49,
tions presently to be mentioned) a fair
illustration Of a hurricane. The dining
table is a large space of the ocean, and the
plate is a vast body Of air several hundreds
of English miles across, which, from some
cause or other, has come into rotatory
motion. The plate, however, is not q
complete illustration. Il fails in two i'm
portant particulars. First, all parts Of
the plate turn round without exception;
while ia the hurricane, or cyclone, as we
may more properly call it, there Is q CEN
trail space which does not turn, but IS
perfectly calm. Secondly the plate
moves round fastest at the edge where
the distance round is greatest, and the
motion becomes slower and slower as
we approach the centre whereas 10 the
cyclone it is the outer edge which moves
slowly, blowing as a stiff breeze, and the
rate of motion increases as we near he
centre, till on arriving at the ring which
surrounds the calm axis, the air rushes
round with a velocity really %fea'ful,
tearing along at so to 90 miles on hour,
le%yelIing buildings and roofing up trees
IN its passage.
The effects OF a severe hurricane strike
us with surprise when w consider that
they are wrought by so soft aud light a
substance as the air. Velocity here
makes up for want Of weight and hardness.
We are reminded of the old experiment
of shooting a candle through a deal board,
or Of that saying Of a great philosopher,
that the globe itself could be split by a
cobweb if only sufficient velocity could
be given to SO delicate an instrument.
Let us return now to the plate on the
dining table. If you wish the illustration
to be as nearly complete as possible it is a
matter Of great consequence uAich coy
you turn the plate. 1t must be turned
in a direction opposite to that taken by
the hands of a watch. This is the law of
all hurricanes north Of tho Equator, and
it is a law which is not merely the result
of observation but can be shewn to
depend on the earth's motion, 50 that it
is as impossible for n hurricane on our sida
cf the equator to turn in the other dlrcc-
ton as it is for the sun to rise In the west.
10 mako our illustration still more corr
rect we must be particular as to the
direction IN uLIch nc more the plate J0rUard
during its revolution. Roughly speaking
this course should be from east to west
but this is only strictly true at the starting
Of the cyclone 10 the Atlantic. AS it moves
EDWARDS, it shecrs off, as it were, towards
The north, so thar when passing Sauto
Cruz, the forward motion OF the storm i:
about ES.E. to W.N.W. The illustration
Of the revolving plate moving forward
will prevent any reader lrom ~confouudipg
this forward motion of the storm "a SOW
movement from 10 to 1G miles an hcut)
with the circular rushing m,tion Of the
air near its axis, We may expand the
illustration by placing small pieces Of
paper, one tenth the width Of the plate
or less, on the table to represent islands.
If now the revolving plate passes over one
of these in its forward motion, we have an
island struck by a hurricane; and il the
centre OF the plate passes over or very
near it, a calamity is represented such as
befelI US in Santa Cruz last September.
Such then is a brief Illustration of what
a hurricane is. It remains to BE- asked
what use can be made of the knowledge.
First we see that the rotation always being
from right to left and the forward
motion invariably from near the east, all
hurricanes in these parts must COM
mence from some point towards the