74 Sir ALEXANDER MACKENZIE

for a solution of the problem. Even the most
- accurate time-piece could not be trusted with-
out frequent correction, and for this there was
usually no opportunity. In consequence the
explorer in distant lands had to fall back on
what were called “absolute”? methods; these
involved first the observation of certain astro-
nomical phenomena, generally the moon or the
satellites of Jupiter, and then the calculation
of Greenwich time from these observations
with the aid of an almanack, by a process
which varied in difficulty in accordance with
the method employed.

Mackenzie, therefore, crossed the ocean
primarily to train himself to take accurate
observations of longitude. He was apparently
ashamed of his results on the first voyage,
though he need not have been in view of
Franklin’s praise, already quoted. He wrote
to Lord Dorchester some years later: “Not
having been furnished with proper instru-
ments to ascertain the longitude on my first
expedition, I made myself but little known
during my residence in London the winter of
1791-2.” This appears to be the reason why,