The H.M. Kala Brass & Steel Pocket Sundial - A Unique Pocket Watch & Sundial Compass in One (Official)

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Evan, Lewis, 'Portable Sundials,' in Gatty, Mrs A., The Book of Sundials (eds. H.K.F. Eden and Eleanor Lloyd) (London, 1900) p.195 It was not until the 13th century that Abul–Hassan introduced the idea of making all hours of equal length and by the 15th century these equal hours were in general use. Renaissance sundials and the French railways

Pocket Sundial by H.M.Kala – Kala Sundial

iii) Scaphe dials: the hour lines are inscribed on the inner surface of a spherical or a conical cup. i) Horizontal dials: the hour lines are laid out on a horizontal plane surface and all converge to the foot of the gnomon that is directed to the celestial pole. Clare Tole-Moir can hardly contain her excitement as she comes across a rare DIY kit dress created by the renowned fashion designer Paco Rabanne. The compass and sundial are both mathematical instruments providing an accurate means of ascertaining time and location. Sundialsii) Cylinder dials: the surfaces bearing the hour lines can be either convex or concave. A common example of this type is the shepherd's dial. Another term for instruments in this category is pillar dial. v) Azimuthal dials: in this type the dial is oriented in such a way that the sun's shadow falls along a specified line, the hour is then indicated by the needle of an in-built compass. The day was then subdivided into 12 parts or 'temporary hours'. Of course the temporary hours would vary in length, being longest in summer and shortest in winter, although in the Mediterranean lands the difference is nothing like as noticeable as it would be in the British Isles. In the latter case an 'hour' in summer would have been twice as long as an 'hour' in winter! A sundial is an instrument specifically designed for determining the hour of the day by projecting the sun's shadow or pinhole image on a set of hour lines. These hour lines can be marked on a flat surface (horizontal, vertical or arbitrarily inclined) or a curved surface (spherical, cylindrical or more complex). The shadow is usually cast by an upright or inclined gnomon (Greek: 'pole') but in some cases a small image of the sun is produced by a suitably located pinhole aperture (which is also termed the gnomon). In this respect a sundial has to be distinguished from the simple gnomon or the meridian line. The latter instruments only determine the exact hour of noon, or, if the meridian line is graduated with a calendar scale, the day of the year. As the Earth rotates on its axis, so the Sun appears to move uniformly across the sky and if a rod is placed parallel to the Earth's axis its shadow will naturally move uniformly around itself. In other words, as the Sun moves through an arc of 15° in the sky in one hour so will the shadow move at the same rate. This is the principle on which most (but not all) sundials are based.

sundial Record ID: SF-BB5242 - POST MEDIEVAL sundial

Pearson, K., 'Walter Frank Raphael Weldon 1860-1906', Biometrika , Vol. 5, No. 1/2. (Oct., 1906), pp.1-52: www.jstor.orgIn additional to conventional sundials, it is also possible to have moon or lunar dials, usually in the form of a sun and moon dial. In principle, a sundial can also be used during the night, provided that the moon is sufficiently bright and that the lunar age is known. The ' solar time' can then be obtained from the 'lunar time' (both expressed in equal hours) by adding four-fifths of an hour for each day of the lunar cycle. In a moondial the correction is effected automatically by adjusting the hour scale for the lunar age.