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How to Set any of these Dials, or any other, tru∣ly upon a Post in a Garden, or elsewhere.
LET the Square in the Figure at the end of this Book, noted with A B C D, be the top of a Post (or other level Plain or Window) upon which you would six your Dial.
About the middle thereof, as at O, describe a Circle, as E G F, and upon O (the Centre) erect a small Pyn or Wire, as O S, exactly perpendicular, and in the Fore∣noon observe when the point of the shadow of the top of the Pyn or Wire touches the Circle, which suppose to be at the point E, (which point mark.) Then again (in the Afternoon of the same day) observe when the sha∣dow touches the same Circle, (which (in the Afternoon) let be at the point F.
These two Observations being made, divide the Cir∣cle between E and F, into two equal parts, which will be at G; so a line drawn from G through O (as the line G O H) shall be a true Meridian line; upon which the Hour line of XII of your Dial must be placed, and the Dial so fixed, (truly Horizontal) shall constantly give you the true Hour.
You may make more Circles than one upon the Plain, lest the Sun upon the same day should not be seen exactly at the same time of both parts of the day, as the Figure plainly shews.