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HE'GIKA, Arab, from hajara, to flee. The 

 epoch or account of time used by Mo- 

 hammedans, who begin from the day that 

 Mahomed escaped from Mecca, 16th July, 

 A.D. 622. The years of the hegira are lu 

 nar ones of 354 days: to reduce them, 

 therefore, Jo our calendar, we must mul- 

 tiply the year of the hegira by 354, divide 

 the product by 365'25, and a'dd 622 ; the 

 result is the Julian year. 



HEIGHT (of an arch) is measured by a 

 line drawn from the middle of the chord 

 or span line to the intrados. 



HEIGHTEN. In painting, to make pro- 

 minent by means of touches of light on 

 brilliant colours. 



HEIR, Norm, heir, from Lat. hares. The 

 person who succeeds another by descent 

 in lands, tenements, and hereditaments. 

 An heir-apparent is one who, on the death 

 of his ancestor, is heir-at-law. An heir- 

 presumptive is he who, if his ancestor 

 should die immediately, would, under 

 present circumstances, be heir, but whose 

 right 'may be defeated by some nearer 

 heir being born. 



HEIR-LOOMS. In law, such personal 

 chattels ae descend by special custom to 

 the heir along with the inheritance of his 

 ancestors. They are generally such as 

 can be taken away without dismembering 

 the freehold, as household furniture, &c. 



HEI/AMYS, the jvmping-rat (&o; and 

 (jut;), called more commonly the jumping 

 hare ; a genus Kodentia. of one species (II, 

 eaffer, F. Cuv.), an animal resembling a 

 hare in size and colour, but having a long 

 tail, and inhabiting deep burrows. Cape 

 Good Hope. 



HELI'ACAL, from yXto;, the sun. An epi- 

 thet applied to stars to express their 

 emerging out of, or their immerging into, 

 the lustre of the sun's rays. Thus a star 

 or planet is said to rise heliacally when, 

 after it has been in conjunction with the 

 sun, and consequently invisible, it gets to 

 such a distance from him as to be seen in 

 the morning before the sun's rising. A 

 star sets heliacally when it goes down in 

 the sun's rays, and is thus invisible. 



HEL'ICAL, spiral ; from A/{, a wreath. 

 Appertaining to the helix of the ear. 



HELIJE'A (Gr.). In ancient history, the 

 chief of the ten courts, among which the 

 6000 Athenian jurymen were distributed. 

 HE'LICOID, tA<, a spiral. In geometry, 

 a curve line generated by supposing the 

 axis of a parabola bent into the circum- 

 ference of a circle, and that the curve is 

 bent correspondingly, every point in it 

 preserving its ordinate distance from the 

 bent axis. The bent curve thus formed is 

 a helicoid. 



HE'LIOCAM'INTS, fatof, sun, and v.at&iies 

 furnace. In ancient architecture, an arched 

 apartment boated by the sun. 



HELiocEN'TRic,from fatof, the sun, and 

 8Tflv, the centre, relating to the centre 

 of the sun. The heliocentric place of a 

 planet is the place of the ecliptic in which 

 the planet would appear to a spectator at 

 the centre of the sun. The heliocentric 

 latitude of a planet is the inclination of a 

 line drawn, between the centre of the 

 sun and the centre of a planet, to the plane 

 of the ecliptic. 



HELIOM'ETER, from fates , the sun, and 

 [Alrqoi, measure. An instrument called 

 also an astrometer, invented by Bouguer, 

 for measuring, with great accuracy, the 

 diameter of the sun, moon, and planets. 

 It is merely a sort of telescope, furnished 

 with two object-glasses of equal focal dis- 

 tance, placed so that the same eye-glass 

 serves for both: hence two images of an 

 object are formed in the focus of the eye- 

 glass, the distance of which depending up- 

 on that of the two object-glasses from one 

 another, may be measured, by means of a 

 micrometer, with the utmost accuracy. 



HE'LIOSCOPE, from fates, the sun, and 

 ffx,OT\ta, to view. A sort of telescope fitted 

 for vie wing the sun without pain or injury 

 to the eyes ; as when made with coloured 

 glasses. 



HELIOS'TATE, from fates , the sun, and 

 a-raro?, settled. An instrument for di- 

 recting the sunbeam steadily to one spot 



HE'LIOTROPE, from fates, the sun, and 

 retfrea, to turn. 1. The name of an old in- 

 strument or machine for showing when 



the sun arrived at the tropics. 2. A 



name of a sub-species of rhomboidal 

 quartz, of a deep-green colour, variegated 

 with biood-red and yellowish spots : hence 

 called blood-stone. 3. A plant, the turn- 

 sole. 



HELIOTRO'PIUM, the turnsole. A genu 

 of plants, Pentandria Monogynia. Name 

 from faiof , the sun, and T^ITM, to turn, 

 because its leaves constantly present them- 

 selves to the sun. Temperate and warm 

 climates. 



HELISPHER'ICAL, spiral; from eA/|, and 

 sphere. The helispherical line is the rhomt 

 line in navigation, so called, because on 

 the globe it winds round the pole spirally, 

 always approaching it, but never termi- 

 nating in it. 



HEL'IX, a spiral line ; from iA/1-, a 

 wreath. Something that is spiral, as the 

 little volute under the flowers of the Co- 

 rinthian capital. The name is applied in 

 anatomy to the whole extent of the auricle 

 or external border of the ear; and in con- 

 chology, to the snail-shell inhabited by a 

 Umax. 



HEL'tEBORrs, the hellebore. A genug 

 of hardy perennial plants. Polyandria 

 Pclyijynia. Name tAAcC0g;, from i 



2 B 



