Evening star. [volume] (Washington, D.C.) 1854-1972, 1909-12-12

West Of the belt. the compass points to
the east of true north.
Were one to pass over the United
States from one extreme corner to an
other. say from Maine to Washington, 1t
would. therefore. be found that the COM
pass direction varied from 20 degrees
west to "a degrees east of north. And
If a similar journey of inquiry had been
made in the year 1850, the compass
direction would have been shown to vary
for the same region from fourteen de-
grees west to nineteen degrees east.
Thus the compass not only points differ
emily at different points on the earth at
any one time, but at the same point it
changes by much as five degrees In
century. In some parts of the earth the
change In a century may be ten degrees
and even more This change in the
earth's magnetism is known as the sec
ular variation
The mariner, the surveyor and the ex-
plorer rely upon the magnetic needle to
guide and serve them for their purp, ses.
They must hence have charts, showing
our globe and by what amount 1t changes
from year to year. The supplying of
magnetic charts and compass data Is one
of the chief objects of the magnetic sur
vey.
Suppose one were to start out from
some place such as New York CITY, for
example, with compass needle in hand
and always follow the direction pointed
out by the north end of the needle. He
would be led across Lake Ontario into
Canada, up along the east side Of James
bay, then across Hudson bay in the d.
rection of Boothia Felix in arctic North
America, where it seems that the north
magnetic pole is at present located AS
the traveller approached this point, how
ever the c0mnaSS would bpcOrnp more
and more tickle and fitful and less and
less strongly inclined to set itself in some
definite direction as 1t had done at the
starting point, or, In other words, it
Right over the magnetic pole the COM
pass would In fact point In any direc-
ton and liz every way: 1t would be of no
more usY there than an unmagnetized
bit of iron or a needle made of brass or
other non-magnetic material. Thus we
see that the force exerted by the earth
as a magrEt upon compass needle be-
comes less and less as the magnetic pole
1t vanishes entirely. How the part of the
earth's magnetic force acting on the COM
pass needle varies over the earth and
how it changes with lapse OF time are
two other lines Of inquiry OF magnetic
survey Of the globe.
If the compass needle fails in the Vi
cinity of the magnetic pole, how would
one tell when he got there? Fortunately
the magnetician has recourse to another
instrument called the dip circle, In which
a magnetized needle Is SO mounted that
it may swing freely in vertical plane
about a horizontal axis instead Of hori-
zontally about vertical axis as is the
case with the compass. At the magnetic
poles the dip needle would stand exactly
vertical. the end which in the compa SIS
points north being in the dip circle down
at the north magnetic pole, whereas at
the south magnetic pole the opposite end
is down.
The greater part of the work of the
Galilee, chartered since 1905. has been in
the Pacific ocean. The Galilee returned
to port in San Francisco some time ago.
after a cruise of nearly three years. In
this time the vessel travelled over 6O,OOO