Bonar Sundial

Most people think that the only purpose of a sundial is to tell the time and that they only work when the sun is able to cast a shadow on the dial's face.  Old sundial's such as this however show that they were once used for much more and were in fact quite exact scientific instruments used for making detailed observations on a whole host of things.   This one is of the equatorial type which means that it was set up at an exact angle parallel to the equator allowing the summer sun to shine on it's upper face and the sun in winter to shine upon the lower, and was used to calculate different events such as Easter and High and Low Tides (1), using complicated systems like the Dominical System (2), the Golden Number (3) and the Epact (4).   (1) Originally the dial had moveable metal arms fitted, one with an eyepiece which could be rotated until the moon was visible through this sight (letting the dial be used even at night).  The dial also had a wind rose which would have been inscribed with the names of different ports around a compass.  Using this device and the position of the moon, high and low tides could be calculated for the different harbours listed on the rose.   (2) The Dominical System was introduced by the Romans and used a series of letters (different letters representing different days of the week) in a repeating system.  It was used to work out various calculations using the Julian Calendar, which had been introduced by Julius Caesar.  It was generally employed between 45BC and 1582AD and only had 365 days in a year. By the date of the manufacture of this sundial it was out by about 10 years.   (3) The Golden Number was a sequence of numbers from 1 to 19 which were used to identify years in a complicated pattern in order to predict Easter.   (4) The Epact was the number of days past the full moon on the 1st of January of a particular year in a 19 year cycle which represented the period before the sun and moon were in the same position in the sky and was also used to predict Easter.   The dial itself is made of slate which was cheap and easily worked and inscribed.  This one has verses and sayings inscribed in both Latin and Scots on such  topics as the weather and the calendar and is covered in astronomical and zodiacal measurements.  The creator, John Bonar, is one of the better known of the 17th Century Scottish sundial manufacturers with several examples of his work still in existence, and in some cases use, in both Scotland and Ireland.  These dials are usually simply known as Bonar Dials.  Bonar was born in 1580 and became a lay preacher in Inverkeithing in Fife.  He was later ordained and moved to Ayr in 1612 where he was employed as Master of the Grammar School where he lived and worked until 1638 and it was during this period that he created his sundials.