Palm House

Perfectly simple: The Campbell-Stokes sunshine recorder

The reason behind last week's venture to the top of the Palm House was check the sunshine recorder mounted on its roof. The irony of tracking hours of sunshine in Edinburgh does not escape me, but it's something staff at the Botanics do every day as part of the observations they collect for the Met Office, the U.K.'s national weather service.

You'd think there would be some sort of technologically sophisticated gadget to record this data, but the reality couldn't be further from that:

This is a Campbell-Stokes sunshine recorder, and in it's analog simplicity it's one of the most beautiful things I've seen at the Botanics. It is just a crystal sphere, held in place with two metal clips, positioned in front of a paper strip. Any sunlight hitting the ball is concentrated by the sphere and burns a mark on the paper behind it. By retrieving the paper each day and measuring the length of the marks one has a fairly accurate record of the day's sunlit hours. Or minutes--this is Edinburgh after all. Different-sized paper strips are used in summer, winter and around the equinoxes to allow for the changing altitude of the sun throughout the year.

Pretty simple, but it works perfectly.