Buys Ballot's Law.
"If you stand with your back to the wind the pressure decreases toward
your left, and increases toward your right."
For navigators, this law is more generally expressed in the words of the
Hydrographic Office on "Cyclonic Storms."
"Since the wind circulates counter-clockwise in the northern hemisphere,
the rule in that hemisphere is to face the wind, and the storm centre
will be at the right hand. If the wind traveled in exact circles, the
centre would be eight points (90 degrees) to the right when looking
directly in the wind's eye. But the wind follows a more or less spiral
path inward which brings the centre from eight to twelve points (90 to
135 degrees), to the right of the wind. The centre will bear more nearly
eight points from the direction of the lower clouds than from the
surface wind."
[Illustration: FIG. 11. SKIRON--THE NORTHWEST WIND]
The law given on the preceding page is named after C. H. D. Buys
Ballott, a Dutch meteorologist. It was announced in a paper published in
the _Comptes rendus_ in 1857. Two American writers on the Winds, J. H.
Coffin and William Ferrell, had however earlier found the law to hold.
* * * * *
While most of us study storms from a window at home and are not called
upon to handle a ship in a storm, yet it may not be out of place to
include here the diagram of the winds in an ideal storm and give the
rules for maneuvering. See Figure 12. The Winds in an Idealized Storm.
The rules apply only to storms in the northern hemisphere.
"_Right or dangerous semicircle_,--Steamers: Bring the wind on the
starboard bow, make as much way as possible, and if obliged to heave-to,
do so head to sea. Sailing vessels: Keep close-hauled on the starboard
tack, make as much way as possible, and if obliged to heave-to, do so on
the starboard tack.
_Left or navigable semicircle_,--Steam and sailing vessels: Bring the
wind on the starboard quarter, note the course and hold it. If obliged
to heave-to, steamers may do so stern to sea; sailing vessels on the
port tack.
_On the storm track in front of center_,--Steam and sailing vessels:
Bring the wind two points on the starboard quarter, note the course and
hold it, and run for the left semicircle, and when in that semicircle
manoeuvre as above.
On the storm track, in rear of center,--Avoid the center by the best
practicable route, having due regard to the tendency of cyclones to
recurve to the southward and eastward."
[Illustration: FROM HYDROGRAPHIC OFFICE