INES IN| ID) | OS

LONGITUDE

In analyzing the results of Mackenzie’s observations it is necessary
to go at some length into the question of longitude in order to see
whether the discrepancy between the results of his observations and
the true position affects his reputation as an observer, and whether his
latitude observations should, in consequence, be rejected.

In order to get a good idea of the matter it may be as well to
discuss the general subject of longitude which, for centuries previous
to Mackenzie’s time, had been the chief bugbear of navigators and
explorers.

The history of the discovery of America gives a very good idea
of the difficulties which arose from lack of accurate data on the subject.
Columbus apparently thought at first that Cuba was Japan, and until
the time of his death, after his third voyage to the New World, imagined
that the mainland of the continent was part of Indo-China, and a
trace of this belief still lmgers in the name of the West Indies, and in
the word Indian, as applied to the aborigines of this continent.

Astronomical determinations of longitude depend on a comparison
between local time and the time at the meridian of reference, which in
this case was Greenwich. Local time, which was obtained by a com-
paratively easy observation on the sun or a star, presented very little
difficulty to Mackenzie; but the correct determination of Greenwich
time was in those days a very different matter, presenting a problem
for the satisfactory solution of which the British Government had, in
1714, offered a reward of £20,000. The first instalment of this prize
was paid in 1765 to a certain John Harrison, who submitted to the
Board of Longitude a chronometer which, after being tested on certain
trial voyages, was retained in England as a model. It is a matter of
local interest to note that the first and third copies of this famous
time-piece were used by Captain Cook on his third voyage, and after-
wards by Vancouver, and so presumably helped in the first published
position of the shores of British Columbia, as well as in the more
detailed chart work later on.

It can be seen then that the satisfactory solution of the longitude
problem, even by ships at sea, was a comparatively recent matter.
Greenwich time could not, however, be carried for any great length of
time by means of chronometers, even when a large number were
transported on board ship under the most favourable conditions.
The timepieces, however carefully they may be rated and compared,
will eventually fail to give the true Greenwich time, and this must be
obtained by some other method. Before the days of telegraph or

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