Some of the changes brought on by the Edinburgh Biomes project might not be what you first think of, because they are small pieces in a much bigger puzzle.

Campbell-Stokes sunshine recorder sits in its cradle on a plinth on a sunny day
Campbell-Stokes sunshine recorder

Recording sunshine

The Horticulture team has assessed all the parts in their work that the project either directly affects or influences, and have made changes where necessary. One of those is sunshine recording, which forms part of our daily data collection for the weather.

Sitting high on the roof of the Temperate Palm House sits a Campbell-Stokes sunshine recorder, which we use to take daily measurements of how much the sun has shone in the past 24 hours.

A crystal ball sits on top of a white plinth, overlooking a garden and glasshouses
High up on top of the Temperate Palm House, the sunshine recorder faces south looking across the Edinburgh skyline

Vintage technology

The Campbell-Stokes recorder is a simple Victorian-era piece of technology that is still in use today, over 140 years after its invention. A solid crystal ball, typically 10cm in diameter, sits in a metal cradle and focusses the sun’s rays onto a photosensitive card. As the sun shines, the concentrated light burns its trace onto the card.

A photosensitive strip of card is held showing a small burn mark
The photosensitive card burns when the sun shines onto it, focussed through the solid crystal ball

Every day for the last thirty years, rain or shine, Senior Horticulturist Bruce Robertson has climbed up on to the roof of the Temperate Palm House to change the sunshine card. During summer, the card is changed at 10am and during winter, it’s changed at 9am. It is especially important to change the card on time on sunny days; otherwise, the sun might burn into the previous day’s measurement.

Part of RBGE’s history

We don’t know exactly when the Campbell-Stokes recorder was first installed on the Temperate Palm House; however, looking closely at one of RBGE’s archive images we can see evidence that it was in position on the southwest corner of the roof walkway at least since 1898.

a black and white of the Temperate Palm House with a zoomed in section showing a detail of the roof
This image of the Temperate Palm House, dated 1898, shows what appears to be the Campbell-Stokes sunshine recorder in the same position as it sits today

Another archive image shows Foreman David Sydney Fish standing by the sunshine recorder in the same position around 1904. The cradle that the crystal ball sits in is a slightly different design so it must have been changed at some point; however, it’s a mystery as to why!

Archive image showing a man standing on the Palm House roof walkway
RBGE Foreman David Sydney Fish standing next to the Campbell_Stokes sunshine recorder, dated c.1904

Palm House restoration

With the closure of the two A-Listed Victorian Palm Houses for their much-needed restoration, the Horticulture team has removed the precious sunshine-focussing crystal ball from its cradle and safely stored it away.

Horticulturist Bruce Robertson holds the Campbell-Stokes sunshine recorder crystal ball
Senior Horticulturist Bruce Robertson removes the Campbell-Stokes solid crystal ball from its cradle in September 2022 after taking one last reading before the Temperate Palm House is restored

With so much history held within its sphere, the Horticulture team plan to reinstate the Campbell-Stokes sunshine recorder back in its place at the completion of the Edinburgh Biomes project.