in Astronomy, an arch of the horizon intercepted between the meridian of the place and the azimuth, or vertical circle passing through the centre of the object, which is equal to the angle of the zenith, formed by the meridian and vertical circle: or it is found by this proportion, As the radius to the tangent of the latitude of the place, so is the tangent of the sun's or star's altitude, for instance, to the cosine of the azimuth from the south, at the time of the equinox.

Magnetical Azimuth, an arch of the horizon intercepted between the azimuth, or vertical circle, passing through the centre of any heavenly body and the magnetic meridian. This is found by observing the object with an azimuth compass.

Azimuth-Compass, an instrument for finding either the magnetical azimuth or amplitude of a heavenly object.

The learned Dr Knight invented some time since a very accurate and useful sea-compass, which is at present used in the navy. This instrument, with another invented by the ingenious Mr Smeaton, answers the purposes of an azimuth amplitude compass. See Compass.

Azimuth Circles, called also azimaths, or vertical circles, are great circles of the sphere intersecting each other in the zenith and nadir, and cutting the horizon at right angles. These azimaths are represented by the rhumbs on common sea-charts, and on the globe they are represented by the quadrant of altitude, when viewed in the zenith. On these azimaths is reckoned the height of the stars and of the sun when not in the meridian.