d with the two lines on the compass. The compass was put on the
middle of the board, and the upper board turned so that the needle was
on a line with the N----S line."

The boys now noticed for the first time that there were two boards, one
above the other, and that the lower one was a little larger, and was
attached to the boat. "Why do you have the lower board attached to the
boat and larger than the upper one?"

"The lower board has on it a section of the compass, and the upper end a
pointer, as you notice, and the line T represents the boat's direction,
so that when the compass was placed on the upper board, the latter was
turned so that it corresponded with the points of the compass. The
little pointer then accurately pointed to northwest, on the lower board,
and by this means the changing of the upper board, so as to keep it due
east and west at all times, will enable us to keep on our course."

It was a long and weary night. One of them slept while the others were
on duty. The boys knew the time on shipboard, where the day begins at
midnight, and is divided into watches of four hours each, thus making
three watches for the night and three for the day. A bell is struck
every half hour, so that each watch is noted by the eight strokes of the
bell. What is called the dog-watches occur between 4 and 8 P.M., this
period being divided in the first dog-watch between 4 and 6, and the
second dog-watch between 6 and 8.

"Why should such peculiar times be taken, or the periods be divided up
in that way?"

"For the very reason that we discussed the arranging of our time of
watch last night; namely, so that one person would not have the same
watch every night. It was agreed by us that one should have three hours'
uninterrupted sleep, while the others were on duty, so that each would
in turn get three hours' work. Our arrangements are somewhat different
from shipboard time, on account of our number, but the principle is the
same."

During the night the wind changed to the north, so that progress was
slow and required considerable tacking, and when the Professor came on
duty he found the course still to the north, and on questioning Harry,
found that the wind had been rather regular during his watch. Within a
half hour of the time he took charge the western shore faded away, and
the course was directed to NWW, in which direction they continued until
well along in the forenoon. Then, as the land receded again, another
tac