Evening star., 1898-05-13
PHENOMENA OF FOG.
Curious Experiences in the Bay and
City of San Francisco.

From the San Francisco Chronicle.
Familiarity with the local phenomena of
fog has destroyed interest in them in The
mind of the average San Franciscan. He
looks with Indifference almost daily
through the summer season on the mar
shaling of the fleecy aerial hosts along the
ocean shore line of the city; of the forcing
by them of the Golden Gate; their assault
of the mission heights; their sweeping
charge over the city; their observation of
the Contra Costa range. and their capture
of the bay. The warning toots of tugs and
steamers and ferryboats; the ringing of
alarm bells at the various ferry landings,
and the doleful cries of the Goat Island and
Point Bonita sirens have to him no special
significance. And yet these familiar fog
phenomena furnished Bret Harte with a
theme for a piece of the finest descriptive
writing that ever flowed from his pen.
Whence comes the great gray bank of
fog that is carried by the strong western
trade winds to the coast line and to the
gates of the city with the setting of the
summer sun is a matter of as much specu-
lation as are the causes of the trade winds
before which the fog bank is driven inland
1t has been inferred that the trade winds
are created by the heating of the great in
terror valleys and the thrush of the colder
air of the sea to supply the vacuum which
the heating process produces. Thus the
ture by solar evaporation far out at sea, is
drawn inshore over the cold northern cur
rent that sweeps down the coast, condens-
ing the Vapor into dense and chilling
fog.
While this phenomenon is present on the
greater part of the coast line it is more
conspicuous in the vicinity of San Fran
cisco than any other part of 1t, which gives
weight to the foregoing theory of Its origin,
as the Golden Gate and the Iow-lying hills
of the San Francisco peninsula furnish an
unobstructed avenue for the aerial currents
from the sea to enter the heated central
basin Of the state, reducing the tempera
ture of both day and night to that pleasant
mean which makes the California climate
matchless among the climates of the earth.
And the dense redwood forests which ex-
tend along the coast from Monterey bay
to the Oregon line draw their SuStenance
from the summer fog drift, for as it passes
through their tail tops, it is held and con-
densed in the embrace Of their branches
into drizzle that drenches the soil in
which their roots are grounded.
In tho winter the meteorological student
finds in the fog drift in San Francisco bay
important and almost unfailng weather
signs. Three consecutive foggy days and
nights are almost invariably forerunners
of a rainstorm. They are usually followed
by a strong southeaster, which drives the
fog out of the hay and brings with 1t the
rainladen clouds that have been formed
in the Gulf of California. to drench the
earth over which they pass.
To the San Francisco fisherman the fog
drift is an open book. He knows through
its signs the condition of the weather in
the outer roadstead without consulting
either the weather bureau or the lookout
at the Point Lobos signal station. If the
bay is full of fog and a strong breeze is
rufRing lis waters he knows that 1t is in
Eine chances out of ten comparatively calm
outside and probably clear. If the fog
hank extends like wall from the Golden
Gate to the Berkeley shore, while the rest
of the bay is clear, he knows that the outer
1cadstead is clear. but banked with fog,
which. later in the day, will be driven in
shore by the trade wind. His movements
and operations are governed largely by
the fog signs with which he is so familiar,
and much Of his immunity from disaster is
due to this fog craft.
When the fog settles on the bay not only
are ali the landmarks shut out of the ferry
masters vision. but the mysterious infiu-
enoa of fog ON the transmission of sound
is 40 deceptive that the location of the siren
SIGNALS and the steam whistles of moving
craft is uncertain and often misleading.
It il actually on record that the sound of
the fog bell at one OF the ferry landings
was not heard on one Of the ferryboats ON
two recent occasions when the nose Of the
boat was within 1CO feet OF the slip. and Q