Hi Dialling Colleagues,
A member of the public (i.e. not a sundial enthusiast) contacted me for help with an item which was sold to him by an antique dealer as a "mid-18th century Chinese sundial". He wanted to know something about it, and particularly how to set it up and read the time. I've put two pictures of the dial at: www.btinternet.com/~john.davis/chinese.htm I have never seen a dial like this before. I would describe it as an ecliptic plane dial, and believe it works as follows: In use, the dial is first placed facing south. Then, on a given day, the elevation of the segment of a circle which comprises the main part of the dial would be set, by the geared mechanism, to put it into the ecliptic plane. Then, the movable radius is adjusted so that it is pointing towards the sun and the shadow of its outer end falls on the centre of the circle. The time is read off a scale on the circumference of the circle, at the rate of 15 degrees per hour. As the segment seems to have an included angle of about 60 degrees, the dial could be used for two hours either side of noon. Has anyone seen a similar dial? Also, can anyone confirm (or dispute) from its general style whether it is really likely to be mid-18th century Chinese? What system of hours was likely to be in use at that time? Happy pondering, John.
