under severall Denominaons, and as an cient as Ptolemy; also fully demonstrated by Clavius in Astrolabio, and by Aquilonius in its own nature. It is also to be seen in an Ancient Author, printed, before ye late contest about its Invention happen’d. Upon ye Supposition mention’d, it follows, if all ye 4. Projections treated off in ye Sector on a qua drant, albeit of different contrivances, and a 5th for findg ye Azimuth in ye limb, wth ye Summer Tropick downwards, are no other yn ye Western sides of ye Horizontall Projec tion, fill’d with more Parallels, and ye Demon straon of ye whole Stereographick Projection may be reduced to a few Proposions more easy than hitherto, rules in likelyhood to be ex spected in ye posthumous works of Tacquet now in ye Press at Anwerp. Here we may observe, yt this Projection is one of ye most easy and speedy Instrunts in its Delinaon, and ye most usefull for findg ye Hour and Azimuth, yt can be made on a sudden w<sup>th<\sup> compasses, especially if thereto be added an exact way for finding Semidia meters of ye Parallels, wth out finding their whole Diameters.
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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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