A Description Of ye double Horizontall Dyall, pre= sented to ye R. Soc. by M. John Collins. It is ye double Horiz. dyal of M. Oughtred, wth some Additions thereto, and some Alterons therein The Cock or Style y<sup>s<\sup> made to unscrew or take off, y<sup>t<\sup> ye lower plate may print, and, if occaon require, may serve for a surveighing Instrument ye Corners being cut off. The Uses of ye Projection etc. are handled in M. Oughtreds sheet annough, and may be reduced to 2. heads. First, if ye Projection be considered only, wthout ye Common dyal and its Cock or Style, then it serves as an Instrument, to give ye suns place, de clinaon, time of rising and setting, length of ye day, and ye amplitude of ye Sun etc. But this dyal differs from M. Oughtreds , in ye placing of ye days of ye month, wch, in his, are set to ye Ecliptick in ye midle of ye projection, but here stand at ye ends of ye parallels of de clinaon, at ye Horizon, and by counting their num ber from ye day of ye month to ye Eqnoctiall ye declinaon of ye [sun symbol] is known; ye houre-line, passing through ye day of ye month, shows ye time of rising and setting, and ye arch of ye Horizon against ye day of ye month shows ye amplitude.
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Description of the double horizontal dial presented to the Royal Society by John Collins, 1667. From The Royal Society, CLP/24/6
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