The San Francisco call., 1897-02-22

of the line between them determined and
made known, SO that a commander may easily
compare the bearing of his compass needle
herewith. This is something that has been
carefully done by Governments, boards of trade
and nautical bodies of Europe, but this valu-
able safeg uard is here being seriously consid-
cred for the first time.
A ships compass is its navigator's most i'm
portant guide, and upon the minute correct
ness of the ships bearing, as told by the CON-
pass, there often depends the chances of safety
and disaster If in the night or the fog the
bearing of the needle and hence of the ship is
fraction of point Tut of the way, the vessel
may strike the reef or the point which
she is steered to clear. The compass
needle rarely points truly on board ship and
it is necessary to know constantly the varia-
ton and the allowances to be made for it
Tne swerving OF the needle from the true
magnetic north dependsupon different things,
and, according to the cause, is called "varia-
tion." deviation" and ''local attraction"
Variation Is due TO the earth's magnetic cur
rents, and being constant in one locality is
known and it is given on the charts. Local
attraction is due to the close presence of large
bodies of iron and is temporary.
Deviation is due to the iron of the ship or
its cargo, and must be known for each vessel.
This deviation varies, too, with the ships
bearing or position. When the ship points
north the needle is affected by the ships iron
differently from what it is when the ship
points east or south. The deviation must be
known, then, for different bearings of the
ship. AS little iron near the compass may
affect the deviation, the deviation should be
known at each sailing 1t is supposed that
the late wreck OF the steamer Humboldt was
due In part to compass deviation. At the in.
vestigation the captain testified that the COM
pass might have been wrong, for there were q
lot of butter boxes piled on deck, and he iron
in them might have affected the needle. Had
the captain of the Humboldt been able TO
easily squint along the line between the shot
tower and some steeple on leaving port and
compared his compass bearing with the known
bearing of that line, the Humboldt might not
have been lost.
The captains of the big ocean-going steam
ers and of deep-water vessels keep careful
track of their compass deviation by the occa-
sional calculation of an aZimuth or ampll-
tude or an observati with polarus, but the
navigators OF coast vessels ignore deviation TO
a great extent, depend on observations of
shores and lights and take chances for the
rest. Many asting captains are not experts
on azimuths, anyway.
By the plan proposed very simple observa-
ton readily taken would enable any coasting
captain TO determine the deviation of his
compass, and that knowledge would be an
other element OF safety to him. 1t would be
convenience valuable to every mariner who
approaches the coast. In Europe and other
countries mountain peaks, rocks, tall chin
neys. church spires and beacons erected for
the purpose are used. What is wanted is two
permanent objects for "transit marks" the
farther apart the better.
About the harbor of San Francisco spires
and all sorts Of prominent objects about the
shore, islands and distant hills would be
taken and along the coast at suitable points,
where hills rise some distance back of the
shore, natural objects or large posts would be
used. The location, description and true mag
netic bearing OF these pairs of objects would
be given to mariners just as buoys, lights, etc.,
are now given. In the harbors these points
would come into line as the vessels swung
with the wind and tide, and at sea captain
could heave his ship to for the brief observa-
ton.
few hundred dollars or so would provide
these aids to navigation from San Diego to
Puget Sound. Messrs. McNevin have ad-
dressed letter TO the Shipowners' Associa-
tion, which will be considered at the next
meeting and it will also comp before the
Chamber of Commerce.