Evening star., 1900-07-07
FACTS ABOUT CYCLONES
SPACE OVER WHICH THEY HAVE
BEEN KNOWN TO FxpAND. .
Remarkable Features ofThis Glass Of
Atmospheric DfstuFbaases - Find
ing the Center Of the Storm.

INm tue Omteu service MaE1Ztnoy.
The theory Of cyclones has during the
last century engaged tthe attention Of a
number of distinguished rineteorolosists.
prominent among whom are Piddington.
Meldrum and Dove, land a considerable
amount Of literature recently published
shows that the subject has lost none Of its
attractiveness either for scientific observ-
ers or for practical men. To give an idea
Of the leading characteristics Of a cyclone
storm We cannot do better than quote the
account given in the Admiralty Manual
upon the subject. published for the guidance
of mariners in general:
The space over which these storms have
been known to expand varies from twenty
or thirty to some hundreds of miles; blow
ing continually round center or vortex,
but with an cvery-varying force, now lull-
ing into little more than q strong breeze
ard then again suddenly swelling up into
uncomfortable fury. But the peculiar char
acteristic Of their revolving action is this:
That in each hemisphere the gyration takes
place in one direction, and that direction
contrary to the apparent course OF the sun,
50 that in the north latitudes these storms
revolve from right to left (or in the oppo-
site direction to the hands of watch and
in south latitudes from left to right Cor in
the same direction as the hands Of a
watch). Another remarkable feature OF
these storms Is their increasing violence IN
the neighborhood of their center or vortex
and yet there they are SO much more f1tful
and uncertain as to render g. vessel help-
less and unmanageable. Besides which, as
she approaches the vortex (unless on the
direct line of its own progressive motion)
the more rapid become the changes Of the
wind, till at length. instead Of veering point
by point as she had found when entering
the storm field, 1t now flies round to the
opposing point-the vessel is taken aback,
or brought by the Ice, in an Irresistible
squall. and forced into sternway against an
overpowering sea.
But besides this circular motion Of the
wind round center, these storms have
bodily progressive movement, rolling on
ward IL 1t may be so osexpressed, along thecr
desolating tracks. sometimes with great
velocity, and sometimes appearing to pause,
or scarcely to advance more than rev
miles in the hour.
The task of the sailor in devising means
what simplified by the fortunate circum-
stance that such storms are fairly method
ical in their habits. In the South indian
ocean, for example. the storms always oc-
cur at the same period of the year, between
December and April; they always originate
about degrees and degrees from the
equator in the eastern part of the ocean,
and pursue course approximately W: W.
fected by the land, and curve away to the
southeast. so that in latitudes Of 25 degrees
and upward the mariner has to ascertain
for himself well as he can the course
followed by the path Of the STORM and
thus some additional degree OF caution Is
required in the higher latitudes.
But the great point to determine is the
probable bearing of the center, and 1t is to
this end that the efforts OF all the OBJ
serves, scientific men and marines alike
are principally directed.
In the old days 1t was customary for the
seaman who suspected,that he was caught
in circular storm to-determine Its center
by sort Of simple mathematical construc-
ton. He conceived his position to be some
where on the circumference Of g. circle.
Upon this circumference ne took the point
the direction Of the wind, and a line drawn
at right angles to this line gave the required
direction. For example. in the southern
| hemisphere the wind being southwest the
direction of the center would be at right
angles to a line so drawn that is. the
bearing of the center of the storm would
be taken as southeast.
This rough-and-ready rule; which was for
many years looked upon absolute
guide, has Of late been accepted with a
certain amount Of reserve. In the Admiral
ty Manual # is stated in a footnote: TT
| must. however. be observed that at a con-
siderable distance from the center and be-
fore the barometer shall have fallen much
below Its normal value. the center may
bear 10 or IL points from the direction of
the wind This view Is emphatically con-
| firmed in the memorandum of Senor Faura,
| director of the Manila observatory. trans
lated for the Annales Hydrogra aphiques,
published by the French admiralty.
He reports: This law 1s erroneous and
is responsible for many disasters" Senior
Faura goes on to explain, as IN the man
ual, that the angle is in general greater
than so degrees, and that Its obliquity
varies not only in different cyclones, but
In different parts Of the same cyclone.
But IL he destroys our faith in the old
time -honored rule, 1t cannot be said that
he gives nothing In return. On the
trary, he formulates a complete system of
rules, based on the indications of the ba-
| rometer. from which he is able to predicate
with absolute certainty both the advent
and the character of the approaching cy-
clone. In fair weather in tropical latitudes
the readings of this instrument are much
more uniform and its variations much more
regular than in parts of the earth more re-
mote from the equator. There is, in fact,
at Manila a species of diurnal atmospheric
tide" such that the mercury reaches its
highest point about to 10 am, and from
4 am. to 8 am. the rise should be not less
than 20 or millimeters, If fair weather is
to be expected. From am. to or per-
haps pm, according to the season. the
level falls, and If the fall Is not greater
than 3 millimeters all is well. From the
| minimum in the afternoon to about 10 pm
a second rise takes place, and the mercury
then falls until a minimum Is again reach
ed at am.
When during rising period the reading
remains uncn anged, or when the rise is
considerably less than Its normal amount
bad weather may be expected. but II dur
| ing a rising period it continues falling as
between am. and o am or from pm.
to 10 pm, then we have unequivocal signs
| that cyclone Is impending. In the words
of SenOr Faura: There Is no time to lose
| the cyclone is certain; 1t is approaching the
point of observation rapidly, and 1t is equal
ly certain to break upon 1t with Violence"
OF the certainty of these barometrical in
dications Faura Is able to remark: This
| rule is so exact that of all the cyclones an
nounced by the observatory Of Manila none
has failed. nor has any cyclone appeared
which has not been previously announced
by this law" second system of indica-
tions is supplied by observations of certain
clouds of the class known technically as the
"cirrostratus." about the time of sunrise
or sunset, which converge toward a point
somewhere near the horizon. From careful
observations Of this point of conveyance
| 1T is claimed that information may be OBJ
tained both as to the position Of the center
and as to the probability of the cyclone
passing over the point of observation. Such
| a system. however. Is probably more suited
sea. 81
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