Philosophical Experiments and Observations by Hooke Robert;Derham W.;

Author:Hooke, Robert;Derham, W.;
Language: eng
Format: epub
ISBN: 1782411
Publisher: Taylor & Francis Group

Dr. HOOK Way to find expeditiously and certainly, the true Meridian; being some what different from the Method in his Posthumous Works, pag 361.

PROVIDE a short Telescope of 1 Foot, or 18 Inches in Length, fitted with a Glass-Plate in the Focus; upon which proper Circles must be drawn, with the Point of a Diamond, for the Pole Star, and two other Stars not far distant from the Pole, which is supposed to be in the Center of this Glass. This Telescope must be sitted with two Plumb-Lines. Now by this Instrument,. in any fair Night, tho’ the Moon shine, it will be very easy to discover the proper Stars, thro’ this Telescope, and to see that each of them be in its proper Circle, about the Polar Point: At which Time, the Axis of the Glass will be in the true Meridian, and, if sitted with the Quadrant, give the Altitude; and the Plumb-Lines being in the Meridian, there may be a Compass suspended by them, which will also shew the Variation easily and certainly. This Instrument is sufficiently intelligible, without any Scheme, which is therefore omitted.

ANOTHER Way is wholly new, and the Observations are made without an Instrument, and the Refractions of the Air do no ways influence either the Observations or Deductions. And that is, by observing, with Plumb-Lines, or other proper Instruments, either both at the same Time, if it may be, or one at one Time, and the other at another, with a true Account of the interposed Time, two Azimuth Lines, in each of which are found two considerable Stars. By the Help of which two Observations, and a true Projection of the Sphere of the Stars, it will be easy and obvious, to any Navigator, to find the Latitude of the Place, the Meridian Line, and the Azimuths of the Stars.

These two Ways were proposed to the Royal Society, April 27. 1687.

W. DERHAM.

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