seamen belonging to a ship, 627 I. The Policy,

Sect. 5. Seamen absenting themselves, II. The construction of the Policy,652
ib. III. Perils of the Sea,

Sect. 6. On the seamen being entitled | IV.

to one third part of their wages

which shall be due, without the

contrary is expressed in the ship's

articles,

ib.

628

Sect. 7. On seamen deserting,

Sect. 8. A vessel of one hundred and

fifty tons and upwards must have a

medicine chest,

THOMAS ARNOLD,

At his Nautical Academy, 295 South Front Street,

Continues to instruct gentlemen designed for and engaged in a seafaring life, in Navigation and Lunar Observations, ascertaining the Longitude by Chronometers and rating them, &c., the Mode of determining the Errors of the Sextant, and its Use, with actual practice, the same as at sea, on very reasonable terms.

T. A. confidently trusts that the experience of thirty years, twenty of which in the practical use of Lunar Observations, has rendered him fully competent to teach the above.

Persons who cannot conveniently attend during the day will be instructed in the evening. Private lessons given if desired.

As the money will be paid on entrance, those who cannot stay to perfect themselves, may return as often as they please, without any additional expense.

EXPLANATION

OF THE

Principle on which the Longitude is obtained

BY

LUNAR OBSERVATIONS.

THE globe, which is 360° in circumference, revolves, on its axis from west to east, once in the course of twenty-four hours.* It is manifest that the meridian of every place on the earth will come opposite to the sun once in that time; and that whenever the meridian of any place comes opposite the sun, it is noon at that place, so that when the meridian of Greenwich comes opposite the sun, it will be noon at Greenwich, and a new day will commence. It must be further observed, that as the motion of the earth on its axis is uniform, equal parts of the equator will pass by the sun in equal spaces of time; and consequently, the one twenty-fourth part of it, or fifteen degrees, will pass by the sun in an hour. Hence, at the end of one hour, after the time when it was noon at Greenwich, the meridian, which is fifteen degrees west of the meridian of Greenwich, will come opposite the sun, and make noon to all places which are on that meridian; and a new day will commence at all those places exactly one hour after it commenced at Greenwich. In like manner, two hours after the time, when it was noon at Greenwich, the sun will arrive

That is, the time from the sun's being on the meridian of any place, to the time of its returning to the same meridian the next day. But the earth performs a complete revolution on its axis in twenty-three hours fifty-six minutes and four seconds. This last is called the siderial day, which is the interval of time from the passage of a fixed star over the meridian of any place, till it returns to it again.