Henry (<[EMAIL PROTECTED]>) asks about doubly-reflecting sunlight through
two mirrors onto a wall.
Why do you need two mirrors? If the wall is invisible from the windowsill
your secondary mirror will have to be huge to catch the first mirror's
reflection throughout the day/year. If it is visible, you can incline the
mirror at an appropriate angle to reflect onto the wall. Calculating the
hour lines will be tricky, but I would suggest plotting them on a sunny day.
Actually, I have designed a reflecting sundial that does use two
reflections, but to achieve something quite different. The secondary
mirror's inclination can be varied so that the spot of light follows the
same path regardless of the declination. Unfortunately, this requires that
the primary mirror be not one mirror but an array of mirrors around a polar
axis, so that each mirror is in use for only an hour or two each day.
Chris Lusby Taylor
