As thus determined it is the angle between the direction of the plumb-line at the place and the plane of the equator.
The most obvious method of realizing this direction is by the plumb-line.
Latitude thus determined by the plumb-line is termed astronomical.
One hypothesis was: while y Draconis was stationary, the plumb-line, from which the angular measurements were made, varied; this would follow if the axis of the earth varied.
It is considered to be an extinct volcano because it makes the plumb-line deviate only 7" to 8", from which it is deduced that the mountain is hollow.
Newton called attention to the fact that a falling body moves in a curve, diverging slightly from the plumb-line vertical.
The deviation from the vertical, was regulated and measured by the introduction of a screw and a plumb-line.
It consisted of a graduated circle inside which another could slide, carrying two small tubes diametrically opposite, the instrument being kept vertical by a plumb-line.
ZENITH (from the Arabic), the point directly overhead; its direction is defined by that of the plumb-line.
It differs from the astronomical latitude only in being corrected for local deviation of the plumb-line.
