There are a number of these around (the one I remember seeing is at the Manor House Museum, Bury St Edmunds) - it's a registered design but I can't remember the details though I think it was 1960s or perhaps later. Basically the cylinder and liquid acts as a cylindrical lens which focuses a bright spot (the intersection of a bright line with the equatorial plane) onto the scale. It only works in summer because it's an upper surface equatorial! It would work with solid plastic or glass but I expect that it is made like that because liquid filled is cheaper ...
Andrew James -----Original Message----- From: Steve Lelievre [mailto:[EMAIL PROTECTED] Sent: 07 June 2000 16:29 To: Sundial mailing list Subject: Water filled sundial at Herstmonceux, England, ... ... photo is at http://www.ualberta.ca/~droles/astro/astrav/Sun2.html
