Fellow dialists,
A few weeks ago there was a thread discussing 'shadow sharpeners' and
the question of the accuracy of the great sundial in Jaipur came up. I was
a bit swamped in marking essays at that point and didn't have time to dig
through some photographs, hunt up references, etc.
I've now got the Archaelogical Survey of India's _The Astronomical
Observatories of Jai Singh_ (New Delhi: Archaeological Survey of India,
1982) before me. The title is correct: observatories, plural. There is a
similar observatory in New Delhi (the Jantar Mantar) which isn't in very
good condition, and there are, or were observatories in Ujjain, Benares
(Varanasi) and Mathura.
The proper name of the great equinoctal sundial in Jaipur is Samrat
Yantra ('Supreme Instrument'). It was constructed around 1734. They give
the dimensions of the instrument as 'being nearly 90 feet high and 147 feet
long' i.e. about 27 metres high and 45 metres long. The radius of each of
the two quadrants is 49 feet 10 inches ( a bit over 15 metres). "It is
graduated to read to seconds, but this is impossible in practice, owing to
the ill-defined shadow". The graduations of the dial are engraved into
white marble slabs which rest on the masonry structure.
The first time I saw the dial, our guide got me to take the lens off
my SLR camera and using it as a 'shadow sharpener' we projected an image of
the sun cutting the gnomon. I remember clearly that it was my first
meeting with the equation of time; our guide had the value for that day in
his head. I was suitably astonished to find, when the correction was made,
that it was just the same as the time shown on my watch.
I'm taking the liberty--with apologies-- of attaching three small
(<20k) images: one of the observatory, and two of the Samrat Yantra. As
can be seen, there are many smaller sundials in the observatory.
One of my favourite instruments is the Nari Valaya Yantra, a huge
masonry equitorial dial at the far right of the overall view. It is of a
form which seems supremely sensible, but which I've never seen used
elsewhere. [Unlike the usual plane versions, there is no difficulty in
using the dial in the winter half of the year]. The Archaelogical Survey
describes it as follows: "The instrument at Jaipur is a masonry cylinder
some 10 feet [3 metres] in diameter. The axis of the cylinder is
horizontal and in the plane of the meridian, and the parallel faces, which
form the dials, are in the plane of the equator." As can be seen from the
fourth scanned image, the dial is actually a small building! The
photograph, taken just about on mid-winter's day, shows the time as about
4pm local solar time.
cheers,
Peter Mayer
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Peter Mayer | [EMAIL PROTECTED]
Politics Department |
University of Adelaide | 'phone:+61.8 8303 5606/5610
Adelaide, SA 5005 | FAX: (+61.8) 8303 3446
AUSTRALIA |
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