Campbell-Stokes sun recorder. Designed to record the hours of bright sunshine by focusing the sun's rays through a glass sphere which will burn a hole through a card.
https://diqn32j8nouaz.cloudfront.net...n_recorder.jpg
Previously:
https://www.homemadetools.net/forum/...115#post157489
https://www.homemadetools.net/forum/...1787#post94713
