“I think not,” added Foster.  “If we steer that course, we should go forty or fifty miles south of Cape Sable, and thus run much farther than we need.  What is the variation?”

“About twelve degrees west,” replied Martyn.

The compass does not indicate the true north in all parts of the earth, the needle varying in the North Atlantic Ocean from thirty degrees east to nearly thirty degrees west.  There is an imaginary line, extending in a north-westerly direction, through a point in the vicinity of Cape Lookout, called the magnetic meridian, on which there is no variation.  East of this line the needle varies to the westward; and west of the line, to the eastward.  These variations of the compass are marked on the chart, in different latitudes and longitudes, though they need to be occasionally corrected by observations, for they change slightly from year to year.

“Variation of twelve degrees,"[1] repeated Foster, verifying the statement by an examination of the chart.  That is equal to about one point, which, carried to the westward from east by north, will give the course east-north-east.

[Footnote 1:  These calculations are merely approximate, being intended only to illustrate the principle.]

The process was repeated, and the same result being obtained, the first master reported the course to Mr. Fluxion, who had made the calculation himself, in the professors’ cabin.

“Quartermaster, make the course east-north-east,” said the first master, when his work had been duly approved by the instructor.

“East-north-east, sir!” replied the quartermaster, who was conning the wheel—­that is, he was watching the compass, and seeing that the two wheelmen kept the ship on her course.

There were two other compasses on deck, one on the quarter-deck, and another forward of the mainmast which the officers on duty were required frequently to consult, in order that any negligence in one place might be discovered in another.  The after cabin and the professors’ cabin were also provided with “tell-tales,” which are inverted compasses, suspended under the skylights, by which the officers and instructors below could observe the ship’s course.

The log indicated that the ship was making six knots an hour, the rate being ascertained every two hours, and entered on the log-slate, to be used in making up the “dead reckoning.”  The Young America had taken her “departure,” that is, left the last land to be seen, at half past three o’clock.  At four, when the log was heaved, she had made three miles; at six, fifteen miles; at eight, the wind diminishing and the log indicating but four knots, only eight miles were to be added for the two hours’ run, making twenty-three miles in all.  The first sea day would end at twelve o’clock on the morrow, when the log-slate would indicate the total of nautical miles the ship had run after taking her departure.  This is called her dead reckoning, which may be measured off on the chart, and should carry the vessel to the point indicated by the observations for latitude and longitude.