The parallel of Declinaon proper to ye day of ye month, cutting ye Ecliptick, shows ye suns place, and ye Houre-circle, y<sup>t<\sup> issuing from ye Pole (as they all doe) pas ses through yt Point, will help you to ye Suns right Accension. If ye Projection be considered as loose, then it may save to take ye suns hight, by sticky a pin upright in ye Center, or in ye Line of East and West, ye shadow thereof falling in ye said line, a thread, with a plummet thereto, hanging from ye Center will in ye limb give ye Altitude sought. When the height is given, ye Author brings y<sup>t<\sup> height, either by Bras-graduated-Index moving on ye Center, or a pair of Compasses wth one foot therein and ye other extended to ye height of ye graduated Index, to meet wth ye Suns parallel, where amongst ye Hours it shows ye time of ye day, and a line from ye Center gives ye Azimuth in ye limb. But on a Print of this Instrument (wch may be very serviceable being pasted upon copper and vernisht) ye want of a pair of Compasses or Bras-index, may be well supplyd by a Thred from ye Center, wth a small Pins-head or Bead on it.
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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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