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

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                                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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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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