Morning journal and courier., 1890-01-20

.ently it could not be depended upon by the

Gently it could not be depended upon by the
mariner to shape course by the shortest
route between two distant points without in
volyipg extensive mathematical calculations
on his part. For the present purpose, then,
it may be said that the first thing a naviga-
tor does on going on long voyage after
making his offing, as It is termed-that ID,
getting clear of land-is to shape his course
to the point of destination or some landmark
on the coast near to 1t. He looks over his
chart to see If there are shoals or rocks or
other dangerous places, and If there be, he d.
rects his course primarily 80 as to avoid
them; If not, the difference in latitude and
longitude between the two ports being taken,
the distance and course can be obtained by
the aid of trigonometry.
The shortest way to any two places on
the face of the globe is not found by follow
ing line upon ordinary Mereator charts
drawn between those places. It is found on
the line of the arch of the great circle, 80
called. which on an ordinary chart wonld
form curved line, tho arch of which would
incline northward at the north side of the
equator and southwark to the south of it.
What Is termed the terrestrial meridian is
the great circle formed by the intersection
of the surface of the earth by the plane pass
ing through the poles and the spot on which
the spectator may be standing, and the FIRST
meridian is the meridian from which longi-
tudes are reckoned.
Now, the idea of great circle sailing is to
secure the shortest route between any two
points between which lorg expanses of sea or
ocean intervene. Heretofore it has been q
very serious matter to work out a great circle
route, for the reason that 1t was necessary to
60 through a great number of mathematical
calculations in order to obtain the various
points for the processes Of the route. On an
ordinary chart, as already said, . great circle
line would appear as curve. Suppose
a course was to be shaped from the Grand
banks Of Newfoundland to Cape Clear, on
the west coast of ireland. Let a straight
line be drawn on the the map for the course
If this were followed, the distance sailed be-
than if sailed on the line of the great circle,
going considerably south of the latter. This
is the fault of the method by which the chart
has been projected.
To give an illustration of how q line
over a convex surface may be q straight
one, as we'll as straight line over plane
surface may be convex one, as shown, it
may pe stated that if a spectator were placed
at the center of the earth, every great circle
on it's surface is bound to cut his eye, and
will consequently appear to him as perfectly
straight lines, whereas, in fact, they are really
curved, and the amount of their curvature
varies according to the distance of the equa-
tor.
On the equator or on the meridian the
ships OF Mercstor track will coincide with
the great circle track, and the course in
either case would be east or west, north OF
south. It follows from this condition of
things that, if chart could be obtained that
was projected on plane surface, on which
the lines were placed in the exact positions
in which they could be seen by an observer
at the center of the earth, we should have
chart on which every straight line, no
matter in what direction 1t was drawn,
is bound to be great circle or sedgement Of
the same.
Now such chart-or rather series of
charts embracing this idea of construction
bas been compiled by the photographic Office
Of the United States in the past few years,
and has been issued in series, the publication
of which, as well, indeed, as the work Of
compilation, is still in progress. the intention
being to make the work as fully exhaustive
as the exingencies of navigation will ever be
likely to call for. That charts of this nature
have long been needed by navigators is well
known, and the lack of euch aids heretofore
has operated against the general adoption Of
the great circle track method of navigation
In other words, the effect of the publication
of these charts will be to shorten long voy
ages by making them on more direct linei
than could be run on the lines of an ordinary
| ,,1opa chart