daylight saving time, on the basis that that's when the sun is most likely to shine, and also that, in the UK, we are on daylight saving for 7 months out of the 12. I also included a 3 degree longitude west offset.
Thus, in use, with the collector positioned pointing due south, at 9:15am, the first FOC is illuminated, at 9:30 FOCs 1 and 2 are lit and so on. At the display end, an increasing number of FOCs are sequentially illuminated, with the last one clockwise indicating local apparent time to the nearest quarter of an hour. Early FOCs eventually go into the shade of the cylindrical collector as the sun progresses. Towards the end of the day, less and less are illuminated.
A bracket was mounted on the baseboard to represent the hole in the side of the house through which the FOCs would be threaded- see Fig 3. In this prototype, collector and display are a mere 450mm apart. In use, the collector would be in the garden, and the display inside the home.
The display (Fig 4) was made using a painted 150mm diameter aluminium clock face, mounted on 8mm plastic board. Some thickness was required to hold the ends of the FOCs securely. The FOCs are a tight sliding fit at each end and are not glued in place. The picture shows the illuminated FOCs at just before 3:15pm - in reality, there is no doubt about the time shown by the FOCs if the sun is shining - the photo doesn't do justice to the
difference between illuminated and shaded FOC ends. It is worthwhile to cut the display ends of the FOCs at an acute angle. This makes the display more readily visible at an angle.
And finally, just in case the sun doesn't happen to be shining, I added a clock movement - you can therefore get the difference between clock and local apparent time. This is the cheating bit!
Several improvements could be incorporated a rotatable collector, thereby adjustable for daylight saving and equation of time changesan increased number of FOCsinterchangeable collector covers with the edge shaped to adjust for the equation of time (two would be needed)Colour filters could be added to add interest
REFERENCES
1. Bull BSS Vol 89/2 Page16
2. Bull BSS Vol 12 (ii) Page 83.
3. Adzema & Jones The Great Sundial Cut Out
Book Hawthorne Books, Inc. New York 1978
