09-07-2011, 10:26 PM
Marco,
Fantastic work as always. As someone who also works bone I have to say too, that the quality of your bonework is stunning!
Sam,
In answer to your question, when the arm is extended it casts a shadow down the side of the cylinder (in daylight that is - sundials cannot be used by artificial light). How far down that shadow extends depends on the angle of the sun and therefore the time of day. This means that by rotating the cylinder until one of the lines carved into it matches the length of the shadow, you can read the time of day according to which line the shadow matches.
It is worth mentioning here that sundials are not a consistent way of calculating time as the the angle of the sun and the length of daylight hours varies according to the time of year, meaning that an hour as calculated in the winter would end up being shorter in actual chronological terms than an hour which was calculated in the summer according to a sundial.
The ancient world did have ways of measuring set amounts of time, such as water containers marked with increments which released water at a steady rate, enabling time to be measured according to the level of water in the container or by using candles of predetermined length and similarly marked with increments which burnt down at a steady rate. Thus it was possible to time something to a specific length of time such as an hour but as the well known example of the hourglass (a later invention I believe), whose action can be started at any time and bears no relationship to the actual time of day, shows, measurement of time alone does not allow one to know the hour of the day. Until the invention of mechanical clocks in the middle ages, the sundial was really the only way to do this.
This particular sundial is quite a sophisticated one, with each of the vertical lines keyed to a particular month of the year. The horizontal lines give approximate hourly divisions for the length of shadow expected for each of these months. This would be fairly good but still nowhere near as accurate as the mechanical clocks which I believe began to appear in the thirteenth century to enable monks to get up at set times of the night (when of course there is no sunlight) to pray.
Crispvs
Fantastic work as always. As someone who also works bone I have to say too, that the quality of your bonework is stunning!
Sam,
In answer to your question, when the arm is extended it casts a shadow down the side of the cylinder (in daylight that is - sundials cannot be used by artificial light). How far down that shadow extends depends on the angle of the sun and therefore the time of day. This means that by rotating the cylinder until one of the lines carved into it matches the length of the shadow, you can read the time of day according to which line the shadow matches.
It is worth mentioning here that sundials are not a consistent way of calculating time as the the angle of the sun and the length of daylight hours varies according to the time of year, meaning that an hour as calculated in the winter would end up being shorter in actual chronological terms than an hour which was calculated in the summer according to a sundial.
The ancient world did have ways of measuring set amounts of time, such as water containers marked with increments which released water at a steady rate, enabling time to be measured according to the level of water in the container or by using candles of predetermined length and similarly marked with increments which burnt down at a steady rate. Thus it was possible to time something to a specific length of time such as an hour but as the well known example of the hourglass (a later invention I believe), whose action can be started at any time and bears no relationship to the actual time of day, shows, measurement of time alone does not allow one to know the hour of the day. Until the invention of mechanical clocks in the middle ages, the sundial was really the only way to do this.
This particular sundial is quite a sophisticated one, with each of the vertical lines keyed to a particular month of the year. The horizontal lines give approximate hourly divisions for the length of shadow expected for each of these months. This would be fairly good but still nowhere near as accurate as the mechanical clocks which I believe began to appear in the thirteenth century to enable monks to get up at set times of the night (when of course there is no sunlight) to pray.
Crispvs
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