sun, and also the direction of the compass itself. In this way the
error of the pointing of the compass as the ship swings around is
found for every direction in which she may be sailing. A table can
then be made showing what the pointing, according to the compass,
should be in order that the ship may sail in any given direction.

This, however, does not wholly avoid the danger. The tables thus
made are good when the ship is on a level keel. If, from any cause
whatever, she heels over to one side, the action will be
different. Thus there is a "heeling error" which must be allowed
for. It is supposed to have been from this source of error not
having been sufficiently determined or appreciated that the
lamentable wreck of the United States ship Huron off the coast of
Hatteras occurred some twenty years ago.





X

THE FAIRYLAND OF GEOMETRY


If the reader were asked in what branch of science the imagination
is confined within the strictest limits, he would, I fancy, reply
that it must be that of mathematics. The pursuer of this science
deals only with problems requiring the most exact statements and
the most rigorous reasoning. In all other fields of thought more
or less room for play may be allowed to the imagination, but here