ADJUSTABLE CYLINDRICAL EQUATORIAL SUN DIAL WITH WIRE STYLE HAVING A REFERENCE MARK FOR FOLLOWING THE VARIATIONS IN THE SUN'S DECLINATION

摘要

A device on a cylindrical equatorial sun dial which can be oriented horizontally and vertically makes it possible: 1) to determine standard time to the nearest minute using a style in the form of a tensioned wire (1) which casts a thin shadow, 2) to determine the months and decades of the year (7) from the vertical displacement on the dial (of sufficient width) of a point shadow formed by a relief reference point (3) located on the wire directly below the equinox, 3) to make an adjustment to correct deviations due to the equation of time. This is done by guided lateral sliding of the cadran along the ''8'' representing the equation of time located on a fixed part (12). The position of the point shadow cast by the reference point indicates the decade of the year, from which the level of the ''8'' and hence the deviation to be compensated can be derived, 4) to obtain a reading in all seasons, including at the equinox, of the time from sunrise to sunset. This is made possible by the shape of the dial, the upper part of which is always horizontal and passes through the plane of the reference point (3), and by the constant orientation toward the local noon. A sheet on which the hour lines are marked is glued to the dial, allowance being made for the difference in order to obtain standard time.