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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Basics of computing sunrise/sunset
From: Douglas Denny
Date: 2009 Jun 18, 11:14 -0700
From: Douglas Denny
Date: 2009 Jun 18, 11:14 -0700
Hello Brad, I would not like to be quoted as being definite about anything on this matter but the best suggestion is that anything before 1910 might be suspect. Sir William Crookes was asked to look into the matter in 1906 and the first Crookes Glass formulations came into being. The report by the Royal Society can be found at:- http://rsnr.royalsocietypublishing.org/content/61/3/301.full The early lab instuments using neutral density filters used literally 'smoked' glass: glass placed in a smokey gas flame where carbon particles adhere. I am not sure about other "coloured" glass of that era for sextants but the only way to be sure is to have spectroscopic analysis done - not easy unless you have friendly university labs available. Regards, Douglas Denny. Chichester. England. ======================= An extract of the R.S. report:- The Royal Society's Glass Workers' Cataract Committee; Sir William Crookes and the development of sunglasses Abstract After the inclusion of a number of industrial diseases and injuries in the Workmen's Compensation Acts of 1896 and 1906, the government asked the Royal Society to investigate how and why glare and heat apparently caused glassworkers to develop cataracts during their working lives. The activities between 1908 and 1928 of the Glass Workers' Cataract Committee, which was made up of chemists, physiologists and ophthalmologists, are discussed. Emphasis is placed on the attempts by the octogenarian William Crookes (PRS 1913?15) to formulate a spectacle glass that was opaque to infrared and ultraviolet radiation. While providing relief for industrial workers, the research also laid the foundation for the modern sunglasses industry. Other significant work of the Committee concerned the biochemistry of the eye. --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---