'While the view from the roof of the glasshouses in the Royal Botanical Gardens Edinburgh was spectacular, I was particularly drawn to the reflections in this Campbell-Stokes sunshine recorder.  The ball acts as a magnifying glass, and burns a dot on the card when the sun is out.  As the sun progresses through the sky, the burn becomes a measurable line, which is interrupted (or totally blank) should clouds block the rays'.

Edition of 20.