C
CABIN to To CALK, or CAULK
CALL to CANNON
CANNON to CANOE
CANOE to To rig the CAPSTERN
Surge the CAPSTERN to CARPENTER of a ship
CARTEL to CATS-PAW
CAULKING to CHANNEL
CHANNELS to CHEARLY
CHEEKS of the mast to CLINCH
CLINCHER-WORK to COASTING-PILOT
COAT to COLLIERS
COLOURS to COMPASS
COLOURS
COMING-TO
COMMAND
COMMISSIONERS of the navy
COMMODORE
COMPANION
COMPANY
COMPASS
COMPASSING to COVE
COUNTER to CRAWL
CREEPER to CROW-FOOT
CROWNING to CUT-WATER
Search
Contact us
COMPASS
COMPASS, an instrument employed to determine the ship's course at sea, and consisting of a card and two boxes. The card, which is calculated to represent the horizon, is a circle divided into thirty-two equal parts, by lines drawn from the center to the circumference, called points or rhumbs. The intervals between the points are also subdivided into equal parts called degrees, 360 of which complete the circle; and consequently the distance or angle comprehended between any two rhumbs is equal to 11�, 15'. The four principal rhumbs are called the cardinal points, deriving their names from the places to which they tend; viz. the two which extend themselves under the meridian, opposite to each other, pointing to the north and south, are called the north and south points. That which is towards the right hand as we look north is termed east, and it's opposite the west point. The names of all the inferior ones are compounded of these, according to their situation. Along the north and south line is fixed a steel needle, which being touched by the load-ftone acquires a certain virtue that makes it hang nearly in the plane of the meridian, and consequently determine the direction of the other points toward the horizon.The compass being of the utmost importance to the purposes of navigation, it is reasonable to expect that the greatest attention should be used in it's construction, and every attempt to improve it carefully examined, and adopted, if proper. Great errors and irregularities, however, have been found incident to the construction of common compasses, arising from the shape of their needles, by which they have not only turned from the true direction, but from that of each other.
The wires, of which the needle has hitherto been generally composed, were only hardened at their ends; now if those ends are not equally hard, or if one end be hardened up higher than the other, when they come to be put together, in fixing them to the card, that end which is hardest will destroy much of the virtue of the other; by which means the hardest end will have the greatest power in directing the card, and consequently make it vary towards it's own direction; and, as the wires are disposed in the form of a lozenge, these cards can have but little force; so that they will often, when drawn aside, stand at the distance of several degrees on either side the point from whence they are drawn; for all magnetical bodies receive an additional strength by being placed in the direction of the earth's magnetism, and act proportionably less vigorously when turned out of it. Therefore when these kind of needles are drawn aside-from their true point, two of the parallel sides of the lozenge will conspire more directly than before with the earth's magnetism, and the other two will be less in that direction: by this means the two former sides will very much impede it's return, and the two latter will have that impediment to overcome, as well as the friction, by their own force alone.
To remedy these inconveniencies, the learned Dr. Knight was induced to contrive a new sea-compass, which is now used aboard all our vessels of war.
 |
Reference Works |  |
© Derived from Thomas Cadell's new corrected edition, London: 1780, page 86, 2003
Prepared by Paul Turnbull
http://southseas.nla.gov.au/refs/falc/0363.html