Description of the double horizontal dial presented to the Royal Society by John Collins

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                                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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Manuscript details

Author
John Collins
Reference
CLP/24/6
Series
Cl.P
Date
1667
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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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