Sundials almost as old as history

Press, 30 December 1978, Page 9

Sundials almost as old as history

The sundial has been used to divide the day into . segments of time since a few centuries B.C. The principle, as indicated by a moving shadow of a fixed marker, known as the gnomon, has never changed but the application has.

Very many of the older gardens used to feature a sundial and one could almost be left with the impression that it was considered to be a necessary inclusion in garden design concepts of the day. Today we find very much less use of this but it can still be used to advantage in variations situations, such as that displayed in the photograph. Initially, the gnomon, from the Greek for “knowing one,” was the first device used to cast a tell-tale shadow of the sun. It consisted simply of a vertical pin and the time was roughly ascertained by the length of the shadow cast. One of the oldest existing dials is an Egyp-

tian shadow clock made of green schist, a crystalline rock. It consists of a flat stone on which is fixed an L-shaped bar,. the short vertical arm of which casts a shadow which is measured by markings on the larger horizontal one. The. Romans and Arabs employed various systems of time telling and the Greeks evolved sundials of greater complexity based on geometries by the Babylonian astronomer Berosus. This man invented the hemispherical sundial or hemi-cycle in which he divided the period between sun-rise and sunset into 12 time periods. These periods were regarded as temporary because of the variations. Armillary spheres were another form of period dating as used by the Greeks. These spheres were used to tell the arrival of the equinoxes and other astronomical phenomena. Originally highly complex instruments, made up of rings repre-

senting the circles (eliptic, horizon, meridian, etc) of the celestial spheres they are now more interesting historically then useful instruments for time telling.

The Renaissance period saw a great boom in sundials, the greatest diversity of styling and form appearing. Great accuracy cannot be expected with the average garden sundial even where considerable effort is taken to establish precisely such factors as the true and magnetic north. Without going to extremes of accuracy, a reasonable time guide can be obtained by following a few simple rules: The selection of the site should be in an open position exposed to full sun from sunrise to sunset. The next step is to establish a perfectly flat base. This is obtained by pouring concrete into a carefully boxed area which should be checked by cross levelling. When the concrete has set the sundial is placed on top.