You mean to say a mariner couldn't determine his heading and range from the light by timing the sweep, compared to an atomic clock?!? Shocking. (. how spoiled we can get with modern navigational aids!)
Dave _____ From: sundial-boun...@uni-koeln.de [mailto:sundial-boun...@uni-koeln.de] On Behalf Of Frank Evans Sent: Thursday, May 17, 2012 3:37 AM To: JOHN DAVIS; Sundial Subject: Re: sundials and tower clocks Small point, John Davis asks why Scottish lighthouse keepers used EoT values engraved on their sundials. Lighthouse lights, like ships' lights, are lit from sunset to sunrise. An error of even as much as five minutes would not matter very much. Frank 55N 1W On 16/05/2012 11:14, JOHN DAVIS wrote: Dear Frank et al, Thank you for the extract from the General Order for lighthouse dials. The thing which surprises me is that it is the EoT value engraved on the sundial that is being taken as the correction figure, rather than one for the date in question published in the current Nautical Almanac. Clearly, only average accuracy could be achieved in this way. Regards, John ----------------------------------------------- Dr J Davis Flowton Dials --- On Wed, 16/5/12, Frank Evans <mailto:frankev...@zooplankton.co.uk> <frankev...@zooplankton.co.uk> wrote: From: Frank Evans <mailto:frankev...@zooplankton.co.uk> <frankev...@zooplankton.co.uk> Subject: re: sundials and tower clocks To: "Sundial" <mailto:sundial@uni-koeln.de> <sundial@uni-koeln.de> Date: Wednesday, 16 May, 2012, 11:01 Greetings, fellow dialists, I know of two particular instances where dials were used to regulate clocks. The first is the noon line of 1829 in the cloister of Durham Cathedral. Obviously its only purpose was to mark the time of noon for the purpose of correcting the Cathedral clocks. The second refers to lighthouses. In a book entitled "From Scotland's Edge" by Keith Allardyce and Evelyn M. Hood the following appears: Since a General Order of 29 January 1852, it has been the practice to have clocks set at local time calculated from sundial readings. The order is precise: "The Lighthouse Timepiece is to be kept right, by observing, if possible, once a week, the indication of the Sun-dial, in the following manner:- The Principal Keeper shall go to the dial, when the sun is shining, and shall watch until the shadow of the style touches any hour, half hour or other time agreed before hand with the Assistant, who shall stand on the balcony, waiting a signal from the Principal. The Principal shall then make the signal, on seeing which, the Assistant shall immediately set the Timepiece to the time already agreed upon. The Principal shall then take a note from the Table of the Equation of Time engraved on the Sun-dial, of the number of minutes by which the clock should differ from the time given by the dial; and shall afterwards proceed at once to the Lightroom where he shall put the timepiece back or forward according as the Clock shall be slower or faster than the Sun at the time. Sundials were universal at lighthouses throughout the UK although they have not all survived, of course. Frank 55N 1W --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
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