AZIMUTH-COMPASS

The brass edge, originally designed to support the card, and throw the weight thereof as near the circumference as possible, is itself divided into degrees and halves ; which may be easily estimated into Smaller parts, if necessary. The divisions are determined by means of a cat-gut line stretched perpendicularly with the box, as near the brass edge as may be, that the parallax arising from a different position of the observer may be as little as possible.

There is also added an index at the top of the inner box, which may be fixed on or taken off at pleasure, and Serves for all altitudes of the object. It consists of a bar, equal in length to the diameter of the inner-box, each end being furnished with a perpendicular stile, with a slit parallel to the sides thereof; one of the slits is narrow, to which the eye is applied, and the other is wider, with a Small cat-gut stretched up the middle of it, and from thence continued horizontally from the top of one stile to the top of the other. There is also a line drawn along the upper Surface of the bar. These four, viz., the narrow slit, the horizontal cat-gut thread, the perpendicular one, and the line on the bar, are in the same plane, which disposes itself perpendicularly to the horizon when the inner-box is at rest and hangs free. This index does not move round, but is always placed on, so as to answer the same side of the box.

Reference Works