Page:Description and Use of a New Celestial Planisphere.pdf/40

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35

Now add the Secants of the Latitude and the Declination to theſe two ſines all into one ſum, which makes - - 19,00069
The half of which will be, - 9,50034
Which is the ſine of — 18° 27'
Which double, or multiply it by 2, and the product is, 36° 54'
Which, convert into time, at 15° per hour, and it gives 2h 27m 36s

Which is the Horary Angle, or the time the Sun wants of being on the Meridian—or it is 32m 24s past 9 o'clock in the morning, for anſwer. And note! the beſt tables for theſe and the Lunar Obſervations, are the Requiſite tables; yet, if they are not at hand, any tables of artificial Sines, Tangent, and Secants will do to ſolve this laſt Problem; but to illuſtrate this Problem ſtill more, and render it perfect in its uſe, both to ſeamen, and others who have no Quadrant, I will ſhew how to take an Altitude by the Planisphere to the neareſt minute, by which the Horary Angle, or time from noon, will come out correct to a ſecond, as thus: on the director is a line called Perpendicular, divided into four equal parts—and a ſimilar line of equal parts, up to ten, on the Hour Circle of ſix, Weſtward; hang the plummet on the center, and let the hair hang over the 12, at night, and then the line of ſix is an Horizon; put a fine pin in the 2, 3, or 4, of the perpendicular lines, and bring this Scale to the Meridian, South, and form a right Angle with the line of ſix, and ſee what diviſion the ſhadow of the