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Tion

sun, sun-dogs, london, dial and seen

TION.

The orientation of the sun-dial after it is made is a necessity of the first importance if satisfaction is desired. This process is carried out usually at night with the aid of two plumb-lines one north and the other south of the position in which the dial is to be set. From the Nautical Almanac the time is found at which the polestar crosses the meridian of the place. The two plumb lines are brought into a line pointing to the star at that moment. The dial can then be placed in the same line conveniently by daylight. It is usual to erect frames of considerable height to hold the plumb-lines so that the sighting upward may he the easier. If the location of the pedestal of the dial is chosen beforehand, the frames for the plumb-lines must be so arranged that both may be moved so as to have the centre of the pedestal in the same line with them and the star.

The sun-dial is daily getting more rare in this age but notwithstanding the superiority of the clock, why has the dial almost everywhere vanished? °If its business use," as has been well observed, °be superseded by more elabo rate inventions, its moral use, its beauty, might have pleaded for its continuance. It spoke of moderate labors — of pleasures not protracted after sunset—of temperance and good hours. It was the primitive clock — the horologue of the first world. Adam could scarce have missed it in paradise. It was the measure ap propriated for. sweet plants and flowers to spring by — for the birds to apportion their silver warblings by— for flocks to pasture and be led to fold by. The shepherd carved it out quaintly in the sun, and, turning philosopher by the very occupation, provided it with mot toes more touching than tombstones."' Denison, E. B. 'Clocks, Watches and Bells' (London 186o) ; Gatty, Mrs. A., 'The Book of the Sun Dial) (London

1900) ; Hogg, W., 'The Book of Old Sun dials' (London 1917) ; Horner, E., (Primitive Sun-Dials or Scratch (Taunton, England 1917) ; Leybourn, W., (London 1700) • Wells, I., 'Sciographia: or the Art of Shadows' (London 1635).

also called and PARHELIOI4. in meteorology, a bright, luminous area sometimes seen on either side and at the same altitude as the sun. Sun-dogs are found at the points in which the solar halos cut the horizontal, parhelic circle. Thus two sun-dogs are usually seen on either side of the sun, and at equal distances from it, though four are not infrequent. The nearer pair are 22° from the sun and the outer are 46° distant, while fainter sun-dogs are more rarely seen at 98° and 120 , and even directly opposite die sun, at 180°. The last is sometimes known as an Anthelion.

Bright areas formed at the intersections of any two circular halos near the sun are some times also referred to as sun-dogs and such sometimes are seen directly above and below the sun. The parhelic circle is produced by the reflection of the sun's light from ice prisms or snow crystals whose axes lie in a vertical po sition: so-called °Contract Arches" arise from prisms whose axes are horizontal. It is the latter that give rise to sun-dogs which are vertically above and below the sun.

Sun-dogs are usually reddish on the sides toward the sun and they are sometimes greatly elongated along the parhelic circle which pro duces them. They vary greatly in brightness and distinctness with the variation of the num ber and arrangement of the ice crystals in the air.