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- A sundial works by using an indicator called a gnomon to cast a shadow onto a graduated surface.
The origins of this system can be traced back to before the first century BC. Sundials were extremely important
for over 1000 years until clocks and watches became accurate and freely available. There are two basic categories,
fixed and portable. It is the fixed dial which can be free standing or secured on, or built into a
building which is
of interest in
conservation terms. Many freestanding dials are
either as individual list entries or by virtue
curtilage rule, and many of those fixed to buildings are
specifically mentioned in list descriptions. They can
be found almost anywhere on castles, cottages,
churches and tombstones. Fixed sundials can be divided into two groups,
horizontal dials which are drawn level with the horizon, or vertical dials which are drawn perpendicular to it. Early
sundials were not particularly accurate because gnomons were set vertically or horizontally, which in theory would only
tell the time accurately on the equator. In early medieval times accurate dials, in which the gnomons were inclined
parallel to the earth's axis to take into account height and direction of the sun, and were capable of indicating hours
of equal length appeared. During the
Renaissance, the science of Gnomics or the Art of Dialling as it
was established as an important mathematical discipline.
Many sundials contain mottos and those fixed to churches often have the times of services marked on them, usually
with a cross. Scratch dials were dials scored onto the walls of churches to indicate the times of services. Sundials,
as well as being carved, were also probably painted onto limewashed surfaces. Gnomons were wood or metal and are therefore
frequently missing on earlier sundials, and it is important to note that the gnomon would not always be contained within
the dial but could be some distance away from it.
Stained glass sundials were relatively common in the seventeenth
century, and those that survive should be particularly treasured as practical combinations of science and art.