degree by meridians is equal to four minutes of clock-time. Multiply the
longitude by four, and the result in minutes is the difference of time
between Greenwich and Aden, 180 minutes, or three hours. When it is noon at
Greenwich, it is three o'clock at Aden, as you see in the diagram before
you."

"Three o'clock in the morning, Mr. Scott?" queried the commander.

"In the afternoon, I should have added. Going east the time is faster, and
_vice versa_," continued the young officer. "At our present speed our
clocks must be put about twenty minutes ahead, for a third of an hour has
gone to Davy Jones's locker."

"I understand all that perfectly," said Miss Blanche with an air of
triumph.

"You will be a sea-monster before you get home. The sirens were beautiful,
and sang very sweetly," added Scott jocosely.

"They were wicked, and I don't want to be one. But I do not quite
understand how you found out what time it was at noon to-day," added the
young lady.

"For every degree of longitude sailed there is four minutes' difference of
clock-time," Scott proceeded. "You know that a chronometer is a timepiece
so nicely constructed and cared for, that it practically keeps perfect
time. Meridians are imaginary great circles, and we are always on one of
them. With our sextants we find when the centre of the sun is on the
celestial meridian corresponding to the terrestrial one; and at that
instant it is noon where we are. Then we know what time it is. We compare