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* HALMOTE. 487 HALO. HALMOTE, or HALIMOTE (from hall + mote. AS. (jrmot. asspmlily ) . An ancient Eniilish court, helil by the lord of a manor for the purpose of aclniinistoring the hiws and customs of the manor. It was composed of the freehoUIers of Iho manor, and came later to be known as the Court Baron or manorial court. See CouBT Babon. HALMSTAD, hiilra'stad. A town in Sweden, and capital of Halland Liin, situated at the mouth of the Nissa on the cast shore of the Catte- gat. about 76 miles south-southeast of Goteborg (Map: Sweden, E S). The town possesses a castle, now the residence of the Governor; a church dating from 1462. and a high school. It is an important railroad centre, and has regular steamsliip connection vith most of the Swedish coast towns as well as with Copenhagen and Liibeck. It is the chief export town for a large part of Southern Sweden. The chief manufac- tures are cloth, beer, and machinery. The town exports lumber, lish (the river abounding in Siilmonl. oats, butter, and woolen goods: the chief imports are food-stuflfs, fertilizers, petro- leum, and Jute. Population, in 1001, 15.400. Halmstad received municipal privileges in 1307, and has been the scene of many important events in the history of Sweden, among them the defeat of the Danes" by Charles XI. in 1076. HALO (Lat. halos, from Gk. a?.u(, halo, disk, threshing-floor, from. dAciu, ftoCei)!, to grind) . The general name given to a class of optical phe- nomena, described more specifically as Globt, CoEON., Aktheli., P.^ehelia, JIock Suns, Sun- DoGS, Paba.seleka, jMock Moons, etc. Mien the light of the sun or moon or bright star shines through a delicate cloud, or layer of fog or mist, a variety of optical phenomena are pioduced which ma.y be classified as (a) circular rings around the sun or moon or star as a centre; (b) horizontal rings around the zenith as a centre; (c) partial arcs around the sun or the zenith; (d) vertical columns of light either through the sun or moon, or through points around the hori- zon symmetrically placed with reference to the hun; (e) elliptical rings around the central lumi- nary. If the observer is so located that his shadow is pro.jected upon a cloud, a bank of fo.g. or a meadow covered with drojis of dew, he may see similar circles of light around his shadow or his anti-solar point, which circles have been described under Anthella. The circles around the sim really occur much more frequently than those around the moon, but are less frequently ob- served, owing to the brightness of the sun; they can, however, easily be seen by viewing the re- flection of the sky in the surface of still water or an nnsilvered glass plate. Halo is the general term by which we designate a variety of optical phenomena whose study is a branch of physical optics. The circular rings of class (a), when they are quite near the sun, namely, within fifteen degrees, and. in fact, usu- ally within five degrees, are the result of the interference of waves of light that have passed around the minute globnles of water, or some- times of dust, in the hazy atmosphere. This process was called diffraction by Sir Isaac New- ton, who showed that in the rear of every small object there is a bright spot instead of a shadow, and surrounding this bright spot a series of con- centric rings or bands of brilliant colors. If one looks at the sun through a mass of small par- ticles or fibres of rather uniform size, as those of wool, a similar series of concentric rings will be seen, the angular diameter of which increases as the diameters of the fibres diminisli ; on this principle Dr. Thomas Young based the construc- tiou of his eriometer for the determination of the diameter of snmll particles and the fibres of tex- tile materials. The largest rings that have been seen about the sun are those known as Bishop's rings, observed after the eruption of Krakatoa. These are about ten, twelve, or fifteen degrees in radius, and must have resulted from the pres- ence of a very delicate layer of the finest imag- inable dust or aqueous globules whose diameters probably did not exceed 0.0002. or one five-thou- sandth of an inch. On the other hand, particles that have a diameter of 0.0013 may produce rings having a radius of one degree, which would, therefore, very closely encircle the sun or moon, whose radius is only one-quarter of one degree. All these circles are known as 'glories.' For large globules of water, such as compose the lower clouds, the difiraction phenomena be- come inappreciable, and are replaced by more complicated phenomena of reflection and refrac- tion. In the higher alto-stratus and alto-cumulus clouds formed of small globules of water the range of diameters is usually rather large, and a series of overlapping circles is seen when the sun or moon is behind them. In the highest cirrus clouds the particles of ice form more delicate circles. For particles of a much smaller size than those that usually occur in clouds, the phe- nomena of dillraction are replaced by the colors of thin plates. Brilliant illustrations of these clouds occurred in the green, blue, and red suns seen when the sun was examined through the clouds of vapor that were thrown off by the eruption of Krakatoa in 18S3. The study of tliis subject led to the experiments by Kiessling, and more especially by Dr. Carl Barus, whose publica- tions on cloudy condensation form the stepping- stones to our present limited knowledge of the growth of minute water-globules from a diameter somewhat less than the tenth of the length of the sodium-wave up to a diameter equal to that wave-length itself. Consult Bulletin No. 12, United States Weather Bureau, 1895. In the small circles or glories referred to, the red circles are outermost, and the blue ones viithin ; the term 'halo' is applied by meteorolo- gists more especially to circles of larger radius formed by reflection and refraction within the drops of water, such as the rainbow and the halos of twenty-two and twenty-five degrees radius. In rainbows or halos formed by one reflection the red is innermost, namely, on the side toward the sun : and the blue is outenno.st, -or away from the sun. Circles formed by two reflections have the red outside and the blue inside. The complex and beautiful halo phenomena that are seen in the winter time result from the reflection and refraction of light by innumerable crystals of ice or simple snowflakes, which pro- duce, in general, a hazy appearance in the air. Wlien the skv is cloudless and of a pale blue near the zenith, these ci-ystals of ice. settling down very slowly throiigh the still air. may be sufTi- ciently numerous to reflect enoiigh sunlight to produce .corgeous efl'ects. The simplest ice crystal is a regilar hexagonal prism whose ends are either planes perpendicular to the axis or