Dialling, plain, concave, convex, projective, reflective, refractive. Shewing, how to make all such dials, and to adorn them with all useful furniture relating to the course of the sun; performed arithmetically, geometrically, instrumentally and mechanically: and illustrated with sculptures, engraven in copper, comprised in XIV distinct tractates... / [William Leybourn].

  • Leybourn, William, 1626-1716.
Date:
1700
Catalogue details

Licence: Public Domain Mark

Credit: Dialling, plain, concave, convex, projective, reflective, refractive. Shewing, how to make all such dials, and to adorn them with all useful furniture relating to the course of the sun; performed arithmetically, geometrically, instrumentally and mechanically: and illustrated with sculptures, engraven in copper, comprised in XIV distinct tractates... / [William Leybourn]. Source: Wellcome Collection.

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    Butbecaufe, as perhaps, through hafte ('and the fhort contraftionofthis, which I had rather have difcourfed than thus made up into a Let ter J any error may have happened in the defigning of the Triangles upon the Horizontal Diagram, take this fecond Solution by the Globe. 2. S 0 L V T I 0 N. The Pole of the Glafs being as by the fifth found, by his Azimuth and Altitude affign a point upon the Globe, by fome piece of white pa¬ per or other thing clapt thereon, from that point with your Quadrant of Altitude ufwally made therewith, or rather Semi-circle oi Steel, Brals,or Whale-bone, application being made to the Pole of the World, Zenith, two points in the Equator and Horizon (becaufe great Circles^ Tropicks, the oppofite equal Arches thereof, lhall give you the refpeftive reflexed points; having always a regard from this point or Pole of the glafs aflign- ed, that you make the Angles of RefleQ:ion equal to the Angles of Incidence. From hence now fome neat Conclufions may be deduced, fuch as thefe: I. Firfl:, That the Sun being at the point D (that is having North De- clinatipn 19 deg. 43 c. t, poft-meridional Azimuth 80 deg. 31c. f- Altitude 32deg. 55C.i, and Hours 41) fliall give a reflexion to P, that is parallel to the Axis of the World, and fo by confequence the Sun in his own pofition to the Glafs (if by obfervation you watch that moment) fhall fhew you the refleded Axis of the Glafe. And fo at London this refieffed Axis is found, when the Sun is in the Meridian having North Declination 13 deg. 6 c. f, the plain of the Glafs lying Horizontal. 2. By this the Superficies of the Glafs, or the Plain of the Glals, appears to be one of the 22 varieties of Plains, and that it declines 60 deg. and reclines 54deg. ^ > 3 That by the plain of the Glafs reprefented in the Horizontal Diagram by V X Y, you have the ,Hour-lines expreflible upon that Plain, or which can be refle6led by that Glafs, and alfo the time of the Year when the Sun will firfl: fhine thereon, and the continuance. 4.1'hat without any Glafs, you may from a point taken, aflign a reflex¬ ed Axis where you pleafe, by an Azimuth and Altitude taken to your own fancy; as fuppofe at D, then will 9 the Pole of your Glafs be found V as before, and you muft be careful in bringing the Center of your Gl^fs into this point, and fo place it, which is alfo very feazible feveral ways. 7. For the practice, or making of thefe Dials, with all the Furniture -thereof (the Theory being thus laid down) I fuppofe you are well enough acquainted therewith; I Ihould propound for my own practice any one of thefe. I. Having got the reflefled Axis, which will always pafs through the Center of the Glafs both into the Air and into the Room [if the tran- fome of your Window lie not direftly in the Meridian] and having erefted a Pafte-board, or fuch like thing at Right-angles thereto, pa- . rallel to the reflefled Equator, you may by Threads defign the Hours, as is now a very familiar practice in making of String-Dials, which ferve both for the Hour of the Day by the Sun, and hour of the Night bv the Stars.