The solar transit This account of the solar compass, and the meridian attachment for transit instruments was written for Young & sons . September, respectively. The Meridian Attachment is simply an instrument made toimitate, on a small scale, the motion of the celestial vault asabove described, consisting of a Solar Telescope revolving aboutits polar axis, wThich corresponds with P C P/, in such a manner,that the line of collimation will follow the sun or any star in itsapparent diurnal motion round the earth. Conversely whenthe transit is turned on its vertical axis to a position where theSol
The solar transit This account of the solar compass, and the meridian attachment for transit instruments was written for Young & sons . September, respectively. The Meridian Attachment is simply an instrument made toimitate, on a small scale, the motion of the celestial vault asabove described, consisting of a Solar Telescope revolving aboutits polar axis, wThich corresponds with P C P/, in such a manner,that the line of collimation will follow the sun or any star in itsapparent diurnal motion round the earth. Conversely whenthe transit is turned on its vertical axis to a position where theSolar Telescope when revolved on its axis will follow the sunor star, its axis must be in the line P C P, and, therefore, in themeridian of the place. This principle was first utilized, but fora different purpose, in the construction of the Universal RingDial, more than a century ago, and a description of that simpleinstrument, will best illustrate the subject for the reason, thatall the many forms of solar attachments are constructed uponthe same principles, and may be said to be mere modificationsof the Ringr Dial. The Ring Fig. 3.—Ring Dial. H O, Horizon; P P, Polar Axis; A Q, Equator;A C Z = P C O, Latitude; Ac b = A c \S, North Declination. The Ring Dial, Fig. 3, consisted of two rings of brass orother metal, which being turned at right angles with each other,corresponded with the equatorial and meridian circles AEOWand O Z H N, Fig. 1, and a plate turning on pivots at p andprepresented the polar axis P C P. In an opening in this platemoved a brass block ^through a small aperture in which thesuns image was projected on a line engraved on the inner edgeof the equatorial circle. The block d could be set to any re-quired declination A C B, by means of graduations along theopening in which it moved. The meridian circle was utilizedas a latitude arc. The dial was suspended from a ring attachedto the vernier / which was set to the latitude of the place, A Z 8 fc r0); JhC ?
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Keywords: ., bookcentury1800, bookdecade1880, bookidsolartransit, bookyear1887
