Page:The New International Encyclopædia 1st ed. v. 05.djvu/280

COMPASS. observed. The division of the compass-card into thirty-two points is a natural one, and was merely continuing the subdivision until it became sufficiently minute. It seems to have been adopted early, as Chaucer writes of it as established in 1391.

Consult: The Admiralty Manual for the Deviations of the Compass, by Capt. F. J. Evans, R.N., F.R.S., and Archibald Smith, M.A., F.R.S. (new editions appear at short intervals); Naval Professional Papers of the United States Navy, No. 22 (Washington, 1886); Cornwell, Compass Disturbance in Iron Ships (1887): Bowditch. The American Practical Navigator (Washington. 1901); publications of the Superintendent of Compasses, United States Navy.

COMPASS, Solar. An instrument for determining at any place an accurate north and south line. It has a latitude range of about 35°, and may be adjusted to the latitude of any place in the United States. It has a latitude are, a declination are, and an hour arc, each to he duly adjusted for an observation, and has been found of much service in running important boundary lines and other Government surveys. One of its recommendations is its avoidance of the perplexities caused by local attraction. It is the invention of William A. Burt. of Michigan. For illustration see Plate of ENGINEERING INSTRUMENTS.

COMPASSES. A mathematical instrument for transferring or marking off distances or for drawing circles. The common compasses or dividers are composed of two rods or legs joined together by a pivot-joint at one end and pointed at the other; when adapted to drawing ares the lower parts of the legs admit of receiving a pen or pencil.

Beam compasses consist of points sliding on a bar, to which they may be clamped at any distance from each other. They are used for lengths greater than the pivot compasses can expand, and when delicately made can be used for more accurate dividing. See.

Proportional compasses have a point at each end of each leg, and the pivot between, thus forming a double pair of compasses opposite to each other. If the pivot is midway between the ends. the opening of each pair of points will be equal. If its distance from one pair of points be double that from the other, the openings will be as two is to one, and so on for any ratio. To adapt them for variable proportions, the pivot is made a clamping screw, which moves in an elongated slot in the legs, and may be fixed at any point.

Triangular compasses have three legs, so that the vertices of a triangle may all be transferred at once.

Bullet or club compasses have a ball in place of one point, adapted to turning in a hole. See also ; (ellipsograph, or oval compasses).

COMPASS-PLANT (Silphium laciniatum). A large plant called also 'resin-weed.' because it abounds in resinous matter. It grows on the prairies, and the edges of its stem-leaves are said always to point directly, or nearly, north or south. When cultivated in gardens, this property does not always appear. The same phenomenon is exhibited by the stem-leaves of prickly lettuce (Lactuca scariola). In this plant the leaves are usually considered as vertical, but this is brought about by a twist near their bases. The peculiar arrangement of the leaves of these plants is due to their adaptation to light. Both surfaces of the leaves are equally sensitive to light, and only by presenting their edges vertically and their tips to the north and south are they able to secure equal illumination to both sides of the leaves.

COMPENSATION. In law, a counterclaim or set-off: in the civil-law systems of Scotland and the Continental States, the doctrine corresponding to that of set-off in the English and American law. It provides that, where two parties are mutually indebted, their debts shall extinguish each other if equal. and if unequal. leave only a balance due. In order to avail one's self of the principle of compensation, the set-off or counterclaim must be pleaded, as it does not operate ipso jure; but, when pleaded, it is held to operate from the period of concourse, the interest on either side being stopped from that time.

Compensatio injuriarum is a defense against actions of damages for slander or the like. It is not a bar to an action. but a set-off or counter-claim. In the common-law system of England and the United States, it is not permissible to set off one trespass or other wrong against another, but each injury must be compensated by a separate action; and in Scotland the leaning recently has been in the same direction. CONTRACT; TORT: DAMAGES; and consult the authorities there referred to.

See COMPENSATION (Lat. compensatio, equalization. from compensare, to equalize, from com-, together + pensare, to weigh, frequentative of pendere, to weigh). A term used in physical experiments to describe methods where sources of error or other conditions are neutralized by the introduction of factors which act in an opposite direction by an equal amount, and compensate for the original error. For example. a flint-glass convex lens, in addition to refracting rays of light, also separates them into their spectral colors. This can be compensated by combining with the convex lens a concave lens of crown glass which has less refraction but greater dispersive power. Such a lens, being opposite in its effect to the first lens, will unite the rays, but does not destroy the deviation. (See ACHROMATISM.) In the case of the pendulum (q.v.), an increase in temperature causes it to lengthen, and consequently oscillate more slowly. Compensation is here effected by raising its centre of oscillation with any increase in length due to a rise in temperature, and thus keeping constant the distance between its point of support and its centre of oscillation. In a chronometer the balance-wheel is compensated by constructing its rim of two metals with different coefficients of expansion. An increase in temperature tending to expand the wheel is compensated by the rim being brought nearer the centre. it being curved inward by the uneven expansion of the metals. See WATCH, for further description and illustration of a compensating balance-wheel.

COMPETENCE, or COMPETENCY. As a law term, used in the sense both of authority and of legal ability. It is in the former sense that