

CV'R 



Horary circles, on globes, are hour 

 lines, or circles marking the hours ; they 

 are drawn at the distance of 15° on the 

 equator from each other. They are the 

 same as meridians. 



HO'RDEIN (Aorrfewm, barley). A ve- 

 getable product found in barley, supposed 

 to exist only in the husk ; it is a peculiar 

 modification of starch. 



HORI'ZON (opiTTo), to bound). That 

 which hounds any thing, particularly the 

 line which bounds our view of the earth 

 and heavens. 



1. The sensible horizon is a plane tan- 

 gent to the globe at the point where the 

 observer is stationed. It is the plane of 

 the circle which bounds our view. When 

 the sun rises, he appears above the 

 sensible horizon ; and when he sets, he 

 sinks below it. 



2. The rational horizon is a plane pass- 

 ing through the centre of the earth parallel 

 to the sensible horizon. It is that line 

 which would bound our view, if we 

 could see at once half the globe. It is 

 represented on the terrestrial globe by 

 the wooden circle which surrounds it. 



HORN. A substance consisting of 

 coagulated albumen and gelatine. It 

 differs from bone in containing only a 

 trace of earth. 



HORN SILVER. Luna cornea. The 

 chloride of silver: the term is derived 

 from its forming a grey semi-transparent 

 mass, which may be cut with a knife, 

 and much resembles horn. 



1. Horn Lead. Plumbum corneum; 

 the chloride of lead, a semi-transparent 

 mass, resembling horn. 



2. Horn Quicksilver. A natural proto- 

 chloride of quicksilver, having a white 

 horn-like appearance. 



HORNBLENDE. Amphibole. A sili- 

 cate of lime and magnesia ; a simple 

 mineral, of a dark-green or black colour, 

 which enters largely into the composition 

 of several varieties of the Trap rocks. 

 There are three varieties, viz., common 

 hornblende, hornblende-slate, and basaltic 

 hornblende. 



1. Hornblende-rock. The primitive 

 greenstone of many writers ; a crystalline 

 compound of hornblende and felspar, not 

 laminar nor fissile, but massive, although 

 generally! disposed in strata. 



2. Hornblende-slate. A primary rock, 

 generally of a distinct slaty structure, 

 composed of crystals of hornblende, often 

 intermixed with felspar, and passing 

 through numerous varieties into acti- 

 nolite-slate. 



167 



3. Hornblende Schist. A term applied 

 by M'Culloch to a variety of mineral ag- 

 gregates in which hornblende abounds, 

 and which are mostly, but not univer- 

 sally, of laminated structure. 



4. Hornblendic Clay-slate. A rock of 

 the Cumbrian group, not composed of 

 hornblende and felspar, like the primary 

 hornblende-slate, but of clay-slate, in 

 which are interspersed crystals of horn- 

 blende and actinolite. 



5. Hornblendic Granite. A variety of 

 granite, in which hornblende is substi- 

 tuted for mica. Frequently, however, 

 both these substances are associated in 

 granite, and the hornblendic gradually 

 passes into the common granite. See 

 Syenite. 



HORNSTONE. A siliceous mineral 

 substance, sometimes approaching nearly 

 to flint or common quartz. It has a 

 conchoidal fracture, and is infusible, by 

 which characters it is distinguished from 

 common felspar. It has been distin- 

 guished into the splintery, the conchoidal, 

 and woodstone. 



HOROLO'GIUM. The Horologe or 

 Clock , a southern constellation, consist- 

 ing of twelve stars. It is cut by a line 

 passing through Canopus to the southern 

 part of Eridanus. 



HORO'LOGY {copa, an hour, Koyoi, a 

 description). A description of the prin- 

 ciples adopted for the measurement of 

 time, and of the various machines em- 

 ployed for this purpose. These comprise 

 the clepsydra and other horologia of the 

 ancients, and the several kinds of watches 

 and clocks of modern times. 



HO'ROSCOPE {wpa, an hour, o-KOTreo), 

 to consider). An astrological scheme of 

 the twelve signs of the zodiac at any par- 

 ticular hour, supposed to indicate the 

 future destinies of any individual by their 

 aspect at the moment of his birth. The 

 signs were called Houses, as being the 

 monthly abodes of the sun, and, besides, 

 every house was appropriated to some 

 planet, every planet having two. In 

 a more particular application the Ho- 

 roscope denoted the point and sign of 

 the Ecliptic which rose above the horizon 

 at the hour in question ; that point 

 was the Ascendant; and the planet to 

 which the sign was appropriated was 

 termed the Lord of the Ascendant, and 

 had its influence over the fate of the new- 

 born child. 



HORSE-POWER. A mode of mea- 

 suring the performance of a steam-engine 

 by reference to the useful eflfect which 



