Directions for making an universal meridian dial, capable of being set to any latitude; which shall give the mean solar time of noon, by inspection, without any calculation whatsoever / By Francis Wollaston.

  • Wollaston, Francis, 1731-1815.
Date:
1793
Catalogue details

Licence: Public Domain Mark

Credit: Directions for making an universal meridian dial, capable of being set to any latitude; which shall give the mean solar time of noon, by inspection, without any calculation whatsoever / By Francis Wollaston. Source: Wellcome Collection.

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    adjustment; but this is the whole of the instrument: which, if carefully constructed, and once rightly fixed in the meri¬ dian, inclined properly according to the latitude of the place (or fitted on a frame, so as to be applied occasionally to a window) will, throughout the year, give the mean solar time of noon, far more accurately than any sun-dial of the usual construction. On this account it is made public : because it should seem it might be convenient in most country places. For it requires no skill in the observer, but merely to see, that his clock or watch point to 12, or to set them to that hour, when the centre of the sun's image is upon the curve line belonging to that month. At present it is not uncom¬ mon to find the clocks in two adjoining parishes, differing nearly half an hour from each other; because so few persons understand rightly the nature of the equation of time, or how to regulate their clocks by a common sun-dial. N. B. The directions above given, contain the principle, and best method of making these dials. But if any person chooses to make use of an impression from the copper plate, which accompanies this paper, he must reduce the radius (or perpendicular distance between the hole in the brass plate and the surface of the paper) according to the pro¬ portion of its shrinking ; that is, after it is pasted on the board and dry, he must consider the whole length of the curve as 0,8684 parts, of which the radius must contain 1,0000.