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Pillar dials

This is one of a series of articles written for "Clocks" magazine by the late Noel Ta'bois, and reproduced with permission here as a memorial to him.

This article originally appeared in Clocks in August 1987

This month's title is yet another gnomonic ambiguity. Pillar dials can be either small and portable or, if out of doors, large and fixed. Most books include the former but I know of only one which mentions both! The portable shepherd's dial, because of its shape, is known also as a column or a cylindrical sundial but the Museums' Committee recommended the term pillar dial. If small enough to be carried in a pocket it is sometimes referred to as a poke dial but this term usually applies to the altitude ring dial shown on this page last June.

A nice specimen of a shepherd's dial which the British Museum kindly allowed me to photograph, is shown in figures 1 and 2. It is French 17th century, made from ivory, and measures 20mm diameter and 93mm high. Being an altitude dial its hour lines are calibrated solely from the height of the sun, like the altitude ring dial.

To allow for the variations in the sun's height with the time of the year, the cap is rotated until the horizontal gnomon is vertically above the date. The months are engraved round the bottom of the cylinder and are divided into approximately ten-day intervals. When not in use the gnomon is folded downwards and stored inside the cylinder.

Further information on the shepherd's dial is included in the 'Clock of Wisdom' article by Charles K Aked in Clocks, February 1987, page 25.

Outdoor pillar dials are any dials mounted on pillars. Common locations for them are in churchyards, where at a glance they may easily be mistaken for churchyard crosses and be passed by, and at village crossroads. A typical example of the latter at Saintbury near Evesham is both a sundial and a cross. It is shown on the Ordnance Survey map but only as a cross. Wouldn't it be wonderful if these maps marked sundials as well!

Keen followers of this page will recall that Saintbury church is one of these which has a Saxon sundial. The church is built on the side of a hill, the main entrance being on the north side. One has to climb further up the hill to reach the rather inaccessible south side on which, of course, a vertical sundial has to be placed. The Saxons chose this location but there is no modern equivalent here. As it was normal in the 19th and 19th centuries for churches to have sundials I looked for one, or evidence of it, in the churchyard but without success. I was, therefore, not surprised to find the pillar dial at the nearby road junction.

Pillars usually carry three or four vertical direct dials to ensure coverage throughout all daylight hours. Because direct dials face the cardinal compass points they are easier to design than declining dials. A single vertical dial can never function for more than 12 hours; only at the equinoxes, or at the equator on other dates, can the theoretical maximum of 12 hours be attained. Depending on the latitude and the sun's declination the number of functional hours is often considerably less than 12.

A pair of very nice pillar dials, similar to the Saintbury dial but without crosses and in a good state of preservation, are to be found one at each end of the hill leading from the church to the castle at Appleby in Cumbria.

The Turnbull or Pelican sundial in the front quadrangle of Corpus Christi College in Oxford is probably one of the finest pillar dials. It is adorned with verses, tables, and sundials of many varieties including, on the column itself, a south facing hour angle sundial, not an altitude dial; the latter is not possible on a fixed column because the gnomon cannot be turned to the sun or adjusted for the date. Two booklets very fully document the Turnbull dial's history and description;: Sundials at an Oxford College and The Pelican Sundial - Description of the Tables both by Philip Pattenden.