Following my remarks on the Pilkington & Gibbs heliochronometer John
Carmichael contributed:
>I'm not familiar with this dial. You don't happen to know where we can see
>a picture of the Pilking Gibbs heliochronometer do you; if not, how about a
>brief description? Why is it so expensive? I bet because it's all
>hand-tooled by you! If this dial were mass-produced using a different
>process would it be possible to lower production costs and make it available
>at a lower price?
>
John,
The P&G dial was a very costly product made up of several large
bronze castings most of which are extensively machined and require
skilled fitting. Typically it was bought for the great houses of the
'Landed Gentry'.
It is basically an equatorial dial turning on a polar axis (adjustable
for any latitude)
There are two metal 'vanes' fixed to the rotating top plate. The one
facing the sun has two small holes, one of which throws a sun image onto
a perpendicular centreline on the lower vane. Compensation for the E of
T is achieved by moving the upper vane sideways by a concealed disc cam
arrangement controlled by a large bronze disc calibrated in months set
against a day sector. The time is read from the edge of the disc against
a minute sector which is adjustable for longitudinal correction.
Two main versions were produced and the Greyscale jpeg I've sent to John
is of the dial in the Science Museum in London. If anyone else would
like to see this 'Rolls Royce of Sundials' there is a 68k jpeg available
on request.
There would be a huge amount of work involved in re-creating the patterns
and the various jigs needed for volume production but I doubt if there
could ever be a sufficient demand to drive the price down - which could
well be much more than my 'off-the-cuff' estimate. I must admit that the
thought has crossed my mind for a 'poor man's version'!
What little I know of this remarkable instrument has been generously
passed on by Graham Aldred who has come to me for replacement/re-scaling
of certain parts during restoration. No doubt Graham will answer any
additional questions there may be.
Best Wishes
Tony Moss
