RECTIFIER

, in Navigation, is an instrument used for determining the variation of the compass, in order to rectify the ship's course. It consists of two circles, either laid upon, or let into one another, and so fastened together in their centres that they represent two compasses, the one fixed, and the other moveable. Each is divided into 32 points of the compass, and 360°, and numbered both ways, from the north and the south, ending at the east and west in 90°. The fixed compass represents the horizon, in which the north, and all the other points, are liable to variation. In the centre of | the moveable compass is fastened a silk thread, long enough to reach the outside of the fixed compass: but when the instrument is made of wood, an index is used instead of the thread.

RECTIFYING of Curves. See RECTIFICATION.

Rectifying of the Globe or Sphere, is a previous adjustment of it, to prepare it for the solution of problems. This usually consists in placing it in the same position as the true sphere of the world has at some certain time proposed; which is done first by elevating the pole above the horizon as much as the latitude of the place is, then bringing the sun's place for the given day, found in the ecliptic, to the graduated side of the brass or general meridian, next move the hour-index to the upper hour of 12, so shall the globe be Rectified for noon of that day; and if the globe be turned about till the hour-index point at any proposed hour, then is the globe in the real position of the earth at that time, if the whole globe be set in the north and south position by means of the compass.