Still, it was by no means indispensable.

For this reason.

When we started, our latitude would be exactly known; and whether, on our voyage westward, we drifted north or south therefrom, we could not, by any possibility, get so far out of our reckoning, as to fail in striking some one of a long chain of islands, which, for many degrees, on both sides of the equator, stretched right across our track.
For much the same reason, it mattered little, whether on our passage we daily knew our longitude; for no known land lay between us and the place we desired to reach.

So what could be plainer than this: that if westward we patiently held on our way, we must eventually achieve our destination?
As for intervening shoals or reefs, if any there were, they intimidated us not.

In a boat that drew but a few inches of water, but an indifferent look-out would preclude all danger on that score.
At all events, the thing seemed feasible enough, notwithstanding old Jarl's superstitious reverence for nautical instruments, and the philosophical objections which might have been urged by a pedantic disciple of Mercator.
Very often, as the old maxim goes, the simplest things are the most startling, and that, too, from their very simplicity.