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History Of Sundials
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Before clocks made their advent, man
needed some devise to know the time of the day, well if not
exactly to the micro second, at least approximately. From such a
need was born the sundial, one of the earliest of the of
timekeeping devices. The time of the day is indicated by the
position of the shadow of an object on which the sun’s rays
fall. As the sun moves across the sky, the shadow also moves,
giving the viewers the exact time of the day.
The gnomon was perhaps one of the
earliest time keeping devices, a device that consisted of a
vertical stick or pillar, the length of whose shadow indicated
the time of the day. It dates back 3500 BC. Some historians have
said that the earliest known sundial was an Egyptian clock,
belonging to the eighth century BC. The device consisted of a
raised crosspiece with a straight base. On the base was
inscribed a scale, with six time-divisions. In the mornings, the
base was placed in an east-west direction, with the crosspiece
at the east end; during the afternoon, the crosspiece would be
placed in the west end. The method employed was simply this –
the shadow of the crosspiece indicated the time. Such primitive
clocks are still said to be in existence. |
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The Berosus sundial, or the hemicycle, was
yet another early sundials and it dates back to 300 BC. It gets its
name from the fact the Berosus, a Babylonian astronomer, devised it.
The hemicycle was usually made of stone or wood and it consisted of
a block, cubical in shape. A hemispherical opening was made in the
block and a pointer was fixed there in such a way that the end of
the pointer lay at the centre of the hemispherical space. The path
of the shadow was a circular arc and the length and the position of
the arc was different in different seasons. Therefore, an
appropriate number of arcs was etched on the internal surface of the
hemisphere. Every arc was divided equally into twelve parts and each
ray had twelve hours. Since the length of the day varied from day to
day and season, they were referred to as temporary hours. This dial,
according to some astronomers, was in use in Muslim countries until as
late as the tenth century. |
A sun dial |
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Sundials devised by the Greeks were more complex. The astronomer
Apollonius used the surface of a conic block, on which the hours
were marked to device a more accurate hemicycle. Ptolemy, another
renowned astronomer, used a device called analemma, which enabled
shadows to be projected geometrically onto flat surfaces inclined at
various angles to the horizontal. The Greeks constructed vertical,
horizontal and leaning dials. All these indicated time in temporary
hours. The Romans also used sundials with temporary hours. Like the
Greeks they had many types of sundials, some of which were portable
too.
It was, however, the sundials devised by the Greeks that fascinated
the Arabs. The Arabs, in fact, attached significant importance to
the study of sundials. After studying the design and the principles,
the Arabs made simplified simpler versions, basing their design on
the principles of trigonometry. It is said that the Arabs were the
first to introduce equal hours (for astronomical purposes). Sundials
with equal hours made their appearance only after the advent of
mechanical clocks. |
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