New-York tribune., 1905-02-20
COMPASS VARIATIONS.

On the back of the Pilot Chart for the cur
rent month is furnished some Information OF
much interest to navigators. Every skilled mari
ner knows not only that the needle py Whlch ne
shapes his course at sea does not point exactly
northward, but also that the extent OF the Varia-
ton Is different in different parts or the ocean,
For these reasons he provides himself with
chart which enables him at a glance to tell now
much allowance he should make at successive
stages of voyage for this singular but familiar
phenomenon Two more novel facts have now
been brought out by several hundred obserVa-
tions taken by experienced officers on transat-
lantic steamships at the request of the Hydro
graphic Office in Washington. One is that wnen
an attempt was made to ascertain the amount
of deviation by sighting a star or other celestial
body the result did not always or often con-
form exactly to expectation. Another is that
the discrepancy, as noted by different ships in
the same part Of the ocean, was not constant
When an average was obtained for large num-
Der of observations some of these errors offset
the rest, thus vlndcating the substantial ac-
curacy of the official estimates OF variation; but
there remained a strong probability that any
individual determination by astronomical meth
DDS would be wrong by at least quarter of a
point" or about three degrees of an arc.
In interpreting the facts Mr.. Littlehales, engi-
neer of the photographic Office, apparently as
attributable to the compasses themselves. When
steel was first substituted for wood in building
ships the indications of the needle were not al
ways trustworthy. To-day the art of compen-
satng for the influence of the metal In the hull
by placing small masses of steel in close prox-
unity to the needle has been carried so far that
such mischief has been abated if not averted.
Mr.. Littlehales feels warranted in believing.
therefore. that the discrepancies under discus
sion result from the inability of ship captains
to determine the amount of variation with pre-
cision They may ascertain their position at sea
exactly If the state of the sky at noon permits
good observation Of the sun, but when they use
that information to compute magnetic eccen-
tricites the result is not satisfactory.
The desirability of making the latter calcula-
ton grows out of the fact that the charts which
captains employ are not always the best. Owing
to the slow secular change IN the earth's mag
netism and to imperfectiOns In past records fire.
quent revision Of the lines showing the compass
variation in different parts of the world is requi
site. Not only should the navigator secure the
latest data concerning this important matter,
but he ought to lend hand in the perfection of
charts. 1t is possible TO do so, first, by acqur-
ing greater skill In determining magnetic varia-
tion by astronomical means. and then by report
ing ones observations TO the photographic or
fee. Much practical good would follow such
service. Sailing by the compass at the present
time means numerous slight deviations from
straight course More accurate knowledge
about the changes in it's detection would save
distance, time and coal.