Thanks to all who have sent in observations on the device my son alerted me to and which I showed at
http://tinyurl.com/5gnqz6 I have been away for a week and only just got back. Apologies therefore for this late acknowledgement to all who responded. The device is, as several suggested, clearly one of the folding versions of the Wheatstone design and identical to one in the Old Royal Observatory Greenwich. A picture of that dial is shown in Allan Mills' article in the BSS Bulletin 98.1 Feb 1998 to which some of you kindly pointed me.. In that article Allan then goes on to describe how to make a modern 'replica' polarisation dial by using sellotape and a black perspex analyser but the interesting thing is that his replica shows a 180 degree time scale divided from 6 to 6 whereas the model I showed and (as may be seen by using a magnifying glass on the image in the BSS article), the one in the Greenwich Observatory too, both have a time scale of 12 to 12. Before I have to set to and make one of these 'replicas' to discover the truth (!), can anyone tell me if there an explanation for this difference between the two designs? Regards Patrick --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
