1IKI.I VCAL 



IIKLMBT. 



ignites limb or member, so that an heir-loom is nothing U but a 

 limb or member of the inheriUnce. (2 Bl. Com.') Chattels are some. 

 Umn diraotod by testators to go to the heir, together with tho inherit 

 anoe, a* heir looms, and though it U the duty of the ezecuton to carry 

 the intention into effect eo far u they ean, yet the direction doe* not 

 affect the righU of onditon, neither can it effectually prereot the 

 devolution of the chattel* according to their real nature. 



HELIACAL (fAiet, the <un), a term applied to the ruing of a star, 

 when it take* place jiut before that of the tun. If we suppose a star 

 not very far from the sun's orbit, then as the *un approaches that star 

 it will become for a season permanently invisible, for it will rue after 

 the sun, and set after it also, the heavens remaining too light in ih. 

 quarter of sunset to permit the (tar to be Men. But u *oon t the 

 orbital motion of the aun hu carried it put the star, the latter will 

 begin to rue first, and in process of time will rue so much before the 

 sun a* to become vuible just before daylight. In thin cane it is said to 

 rue heliacally : thiu a itar aeU heliacally before it* aeaaon of dis- 

 appearance, and risen heliacally after iU reappearance. The successive 

 heliacal risings of stars thus form a continued warning of the seasons, 

 and were used for this purpose among eome ancient nations. But 

 since the preceasion of the equinoxes slowly changes the offices of 

 different stars with respect to the seasons, an ancient record of the time 

 of the year when a given star rose heliacally would enable us to make 

 a rough guees at the number of centuries elapsed since the time of the 

 observation. Upon such a basis Newton rested a great part of his 

 system of chronology, taking the descriptions of the heliacal risings of 

 stars from Hesiod. 



HELIACAL CURRENTS. [ELECTRO-DYNAMICS; ELECTRO-MAG- 

 NETISM.] 



HKLICIN. [SALICTL.] 

 HEI.K'olIH.V (SuicYl..] 



11 Kl.lt )< 'KNTKIC (having the sun as centre), a term applied to the 

 place of a planet, as seen from the centre of the sun, in opposition to 

 its geocentric place, as seen from the centre of the earth. [PARALLAX.] 

 HKUOMETER (*\m, the "sun," and ftrrpw, " measure ") is the 

 name given by M. Bouguer to a micrometer invented by himself about 

 1745, by means of which the diameters of the heavenly bodies may be 

 measured with considerable accuracy. In Bouguer's construction the 

 tube was of a conical form, and provided with two object-glasses of equal 

 focal length, which were so adjusted as to admit of being moved in a 

 direction transverse to the axis of the tube ; or the object-glass was 

 cut into two parts through a diameter, these two parts being relatively 

 moveable. By this contrivance the two images which are formed in 

 the focus of the eye-glass may be made to diverge, coincide or lap 

 over each other, by merely varying the distance .between the centres 

 of the object-glasses, and this distance is indicated by a graduated 

 scale attached to the tube. When the two images coincide, the 

 angle subtended by the observed objects will be equal to that 

 subtended by the centres of the object glasses, which being known, 

 the magnitude of the observed object may readily be computed 

 when its distance is given, or the distance determined when its 

 magnitude is given. As this instrument does not differ in principle 

 from the divided object glass micrometer, the reader U referred to the 

 article MICROMKTFR ; and for further information relative to the in- 

 vention, see the ' Me'moires de ('Academic Royale des Sciences,' 1748, 

 p. 1 1. [Bocoi'ER, in Bioo. Drv.J It is necessary, however, to refer 

 to the noble instrument at Oxford, constructed by M. Repsold, and 

 placed under the management of Professor Johnson. This heliometer 

 is mounted as an EQUATORIAL, with the hour-circle at the top of the 

 pillar, and the declination circle at one end of the axis, both witliiti 

 reach of the observer. The divided object-glass is 76 inches in din- 

 meter, and has a focal length of 10-5 feet It is cut into two semi- 

 circles by a section along a diameter, and the two pieces are made to 

 slide along their common section by means of micrometer screws, con- 

 nected with graduated scales. Rather than attempt to describe this 

 instrument and the valuable work performed by it, which would be 

 necessarily imperfect in our limited sp ice, we think it best to refer to 

 the ' Radcliffe Observations ' for 1851, in which volume, and the pre- 

 vious one, the structure and use of the Oxford heliometer are ably 

 ,\\~~,,mm~A by Professor Johnson. There is also the celebrated memoir 

 by Besnl in the ' Konigsberg Observations/ and the dissertation by 

 Bmnow In hit ' Spazische Astronomic.' 



HK'LIOS ("HAioi), In the Greek, Sot in the Roman, mythology, the 

 un-god, was the son of Hyperion and Theia, or of Hyperion and 

 Euryphaensa. Homer speaks of Helios as ascending the sky daily from 

 Oceanus to give light to gods and men, and again descending by the 

 western gate. Later writers enlarge much on the glory of his abode ; 

 or describe him as nailing during the hours of the night round half the 

 globe in a vessel of gold, the gift of Hephicstus, and wrought by his 

 hands, or softly sleeping on a golden couch. The chariot of Helios was a 

 quadriga ; his horses fed upon herbage growing in the blissful isles. By 

 Homer, Helios is spoken of as seeing all that is done by men and gods, 

 and hence he was able to give notice to Demeter of the abduction of her 

 daughter Persephone, and to warn Hcphicstus of Aphrodite's infidelity. 

 His Bocks were kept in the sacred isle of Thrinacia, in Sicily. Temples 

 appear to have been erected to Helios in many parti of Greece ; bulls, 

 horses, goats, rams, and other animals, usually white, were sacrificed 

 to him. Helios was especially honoured at Rhodes. Representations 



of him were engraven on the coins, both full-faced and in profile, 

 surrounded with rays of light, or having streaming ray-like hair. The 

 famous Colossus of Rhodes was a status of Helios, 70 cubiU high. In 

 the later ages Helios was to a great extent confounded with APOLLO. 



1 1 K LIOSCOPE (a Greek terra signifying literally " sun-observer ") U 

 a kind of telescope, adapted for making observations upon the sun 

 without the eye being injured by the intense brightness of the solar 

 rays. Dr. Hooke wrote a treatise in 1742 expressly on the subject of 

 helioscopes, wherein he recommends four reflecting-glaases to be so 

 placed within the tube of the telescope that the soUr rays may suffer 

 four reflections before they strike the eye , and thus, he observe 

 intensity will be reduced to the 256th part of their original intensity. 

 Hevelius and other philosophers preferred the use of coloured glasses, 

 which is the common practice of the present day ; while Huygens 

 merely blackened the inner side of the eye-glass by holding it over the 

 smoke of a lamp or candle. 



HELIOSTAT, an instrument used for making a solar beam appear 

 stationary, or rather preserve an invariable dinvtion, notwithstanding 

 the motion of the sun in the ln.ivrn*. Such an in-tnini' nt is neces- 

 sary to persons engaged in the higher branches of optical research, and 

 its principle rests on that of the EVJI-ATOHIXI.. There is a reflecting 

 surface connected with a polar axis, which U moved by clock-work at 

 the rate of the sun's diurnal velocity, so that the ray thus reflected is 

 constant in direction : whence the name of the instrument, from *Aio 

 the sun, and urrqpi to stand still Of course the ray thus obtained may 

 be received by a second mirror, and turned in any required dir. 

 There is a good description of a heliostat in the second volume of Biot's 

 ' Precis Elementaire de Physique,' also in Pouillet's ' Physique/ and 

 Frick's ' Pbysikolische Technik." 



HELIOTROPE, an instrument used, chiefly abroad, in geodetic 

 surveys, to enable the surveyor to transmit signals of reflected light 

 from one station to another, and to perceive with facility the signals 

 transmitted. M. Merz, of Munich, is said to have contrived the most 

 convenient form of this instrument. 

 IIKLIX. [SCREW.] 



HELLEBORINE. A vegetable alkaloid of unknown composition 

 contained in the root of the black hellebore. It resembles piprrine. 



HELLEBORUS NIGER (Black Hellebore, or Christmas Rose.) The 

 root of 11. Niger is now the officinal one, and it is to be regretted that 

 many other roots, especially those of Acttea tjricata and Adomii ternalii, 

 are often intentionally or accidentally sold in its stead. These may be 

 discriminated by physical characters (particularly the internal struc- 

 ture), and by chemical tests. The activity of hellebore seems to 

 n its resinous matter, for which rectified (not proof i .-pirit is the 

 proper menstruum. 



Like most ranunculaccous plants hellebore can occasion ruin-faction 

 and inflammation of any surface with which it is brought in contact; 

 when taken into the stomach in a moderate dose it gently stimulates 

 it and the other viscera of the abdomen ; but in large doses it is a fatal 

 poison. It is a dangerous medicine, and one which is rarely necessary 

 to have recourse to. 



The hellebore of Hippocrates, Dioscoridcs, and other ancient writers, 

 famous for the cure of insanity, U not the plant mentioned above, 

 which is a native of southern Germany, the Apennines, also of Laconia 

 and Mount Athos. The plant of the ancients is called by I ' 

 thorp, H. afficinalu, by Decandolle, H. oriental'a; it is found on Mount 

 Olympus, Helicon, aud the island of Anticyra. Its purgative pro- 

 perties occasionally rendered it useful in madness. 

 HKLLENENE. |ll 



HKU.KNI.V ((', 1 1 _.,()) is a concrete volatile principle, allied to the 

 essential oils. It is a solid .ry.-t.illine body, ainl i.~ ..l.t iin,J from the 

 Innln 1/tlrnium. With nitric acid it yields niln-fiellaiiti, whilst 

 inli vdrous phosphoric acid converts it into a hydrocarbon helhnrne 

 CJELA 



HKLM WIND. [\Vixn.] 



HELMET, an ancient armour of defence for the head, still worn by 

 the officers and soldiers of some of our cavalry regiments. Its original 

 name was Helm, possibly borrowed from the Latin (of the lower age) 

 \tlmtii. Skinner however derives it from the Anglo-Saxon verb helar, 

 ' Helm" certainly occurs botli in Odmon's 'Paraphrase/ 

 and in the Saxon Gospels, as well as in .Klfiic'w <ll.,.xuy.' Jfelmet 

 was probably adopted, in the middle age, from the Italian </ 



An a part of defensive armour the helmet is of high antiquity : some 

 sort of covering of this description for the head appears to have been 

 worn by the warriors of every country. Helmets were found even 

 among the inhabitants of tho South Sen Islands when disc"vcivd i-v 

 Captain Cook. Among the oldest specimen* nmv n-m. lining are pro- 

 Ualily the two helmets found mi tin: field of r.inna- in M~>1, preserved 

 in s.i \Villi:im Hamilton's collection in the I. .: i. Museum. An 



helmet, bearing 'iynipia, was pre- 



sented to the British Mnxeuni l.y Kin- Ctxirge IV. 



The form of the Greek helmet and its general description may be 

 collected from various passages of the Greek writers, from Homer 

 downwards, and more especially from the medals and marbles on which 

 it Is represented. We give the representation of one from a terra-cotta 

 in the Townley Collection in the British Museum, showing the beads 

 of Athene and Zeus. In the same collection ore others of Athene, 

 and also one of Pericles. It does not appear that the Greek or Roman 



