it is only an
approximation, after all, to be corrected by one's own judgment from
data of a thousand voyages; and even then the master of the ship, if
he be wise, cries out for the lead and the lookout.

Unique was my experience in nautical astronomy from the deck of the
_Spray_--so much so that I feel justified in briefly telling it here.
The first set of sights, just spoken of, put her many hundred miles
west of my reckoning by account. I knew that this could not be
correct. In about an hour's time I took another set of observations
with the utmost care; the mean result of these was about the same as
that of the first set. I asked myself why, with my boasted
self-dependence, I had not done at least better than this. Then I went
in search of a discrepancy in the tables, and I found it. In the
tables I found that the column of figures from which I had got an
important logarithm was in error. It was a matter I could prove beyond
a doubt, and it made the difference as already stated. The tables
being corrected, I sailed on with self-reliance unshaken, and with my
tin clock fast asleep. The result of these observations naturally
tickled my vanity, for I knew that it was something to stand on a
great ship's deck and with two assistants take lunar observations
approximately near the truth. As one of the poorest of American
sailors, I was proud of the little achievement alone on the sloop,
even by chance though it may have been.

I was _en rapport_ now with my surroundings, and was carried on a vast
stream where I felt the buoyancy of His hand who made all the worlds.
I realized the mathematical truth of their motions, so well known that
astronomers compile tables of their positions through the years and
the days, and the minutes of a day, with such precision that one
coming along over the sea even five years later may, by their aid,
find the standard time of any given meridian on the earth.

To find local time is a simpler matter. The difference between local
and standard time is longitude expressed in time--four minutes, we all
know, representing one degree. This, briefly, is the principle on
which longitude is found independent of chronometers. The work of the
lunarian, though seldom practised in these days of chronometers, is
beautifully edifying, and there is nothing in the realm of navigation
that lifts one's heart up more in adoration.

CHAPTER XII

Seventy-two days without a port--Whales and birds--A pe