VERTICAL

, something relating to the vertex or highest point. As,

Vertical Point, in Astronomy, is the same with vertex, or zenith.—Hence a star is said to be Vertical, when it happens to be in that point which is perpendicularly over any place.

Vertical Circle, is a great circle of the sphere, passing through the zenith and nadir of a place.—The Vertical circles are also called azimuths. The meridian of any place is a Vertical circle, viz, that particular one which passes through the north or south point of the horizon.—All the Vertical circles intersect one another in the zenith and nadir. |

The use of the Vertical circles is to estimate or measure the height of the stars &c, and their distances from the zenith, which is reckoned on these circles; and to find their eastern and western amplitude, by observing how many degrees the Vertical, in which the star rises or sets, is distant from the meridian.

Prime Vertical, is that Vertical circle, or azimuth, which passes through the poles of the meridian; or which is perpendicular to the meridian, and passes through the equinoctial points.

Prime Verticals, in Dialling. See Prime Verticals.

Vertical of the Sun, is the Vertical which passes through the centre of the sun at any moment of time. —Its use is, in Dialling, to find the declination of the plane on which the dial is to be drawn, which is done by observing how many degrees that Vertical is distant from the meridian, after marking the point or line of the shadow upon the plane at any times.

Vertical Dial. See Vertical Dial.

Vertical Line, in Dialling, is a line in any plane perpendicular to the horizon.—This is best found and drawn on an erect and reclining plane, by steadily holding up a string and plummet, and then marking two points of the shadow of the thread on the plane, a good distance from one another: and drawing a line through these marks.

Vertical Line, in Conics, is a line drawn on the Vertical plane, and through the vertex of the cone.

Vertical Line, in Perspective. See Vertical Line.

Vertical Plane, in Conics, is a plane passing through the vertex of a cone, and parallel to any conic section.

Vertical Plane, in Perspective. See Plane and Perspective.

Vertical Angles, or Opposite Angles, in Geometry, are such as have their legs or sides continuations of each other, and which consequently have the same vertex or angular point. So the angles a and b are Vertical angles; as also the angles c and d.