HEL 



HEL 



so that the vertical diameter is extended, 

 or appears longer, than the horizontal di- 

 ameter. 



HELIOCENTRIC latitude of a planet, 

 the inclination of a line drawn between 

 the centre of the sun and the centre of a 

 planet, to the plane of the ecliptic. 



HELIOCENTRIC place of a planet, in astro- 

 nomy, the place of the ecliptic, wherein 

 the planet would appear to a spectator 

 placed at the centre of the sun. 



HELIOPHILA, in botany, a genus of 

 the Tetradynarnia Siliquosa class and or- 

 der. Natural order of Siliquosae Crucifor- 

 mes. Cruciferae, Jussieu. Essential cha- 

 racter : nectaries two, bowed back tow- 

 ards the bladder of the calyx. There are 

 ten species. These plants are all natives 

 of the Cape of Good Hope. 



HELIOSCOPE, in optics, a sort of te- 

 lescope, peculiarly fitted for viewing the 

 sun, without hurting the eyes. See TE- 

 LESCOPE. 



HELIOTROPE, in mineralogy, a spe- 

 cies of the flint genus. It is of a green 

 colour, and occurs massive, in angular 

 and rolled pieces; it is commonly trans- 

 lucent on the edges ; the specific gravity 

 from 2.6 to 2.7. It is found in rocks, 

 and is said to be the connecting link be- 

 tween jaspar and chalcedony. In Asia, 

 it is found in Bucharia, Persia, and Sibe- 

 ria ; and in Europe, in Iceland, and in 

 Upper Saxony. From the beauty of the 

 colour, and its great hardness, it is reckon- 

 ed of great value among lapidaries, and 

 that which has the greatest degree of 

 translucency, and most numerous red 

 spots, is of most value. 



HELIOTROP1UM, in botany, a genus 

 of the Pentandria Monogynia class and 

 order. Natural order of Asperifoliae. Bor- 

 raginese, Jussieu. Essential character : 

 corolla salver-shaped, five-cleft, with 

 teeth interposed; throat closed with 

 arches. There are twenty-four species, 

 of which H. Peruvianum, Peruvian turn- 

 sole, or heliotrope, is a small shrubby 

 plant, from two to three feet in height ; 

 the leaves are long, hairy, and much 

 veined, of an ash-colour on their under 

 side, on short foot-stalks ; the flowers 

 are produced at the ends of the branches, 

 in short reflex spikes, growing in clus- 

 ters ; the peduncles divide into two or 

 three, and these again into smaller ones, 

 each sustaining a spikelet of pale blue 

 flowers, which have a strong, sweet 

 odour, somewhat resembling bitter al- 

 monds. It grows naturally in Peru ; it 

 flowers with us great part of the year, 

 and those flowers which come out early 



in the summer, are succeeded by ripe 

 seeds in autumn. 



HELIX, in geometry, the same with 

 SPIRAL, which see. 



HEMX, in natural history, the snail, a 

 genus of the Vermes Testacea class and 

 order. Animal a Umax ; skell univalve, 

 spiral, subdiaphanous, brittle; aperture 

 contracted, semi-lunar or roundish. Of 

 this genus more than three hundred spe- 

 cies have been enumerated; they are se- 

 parated into divisions ; A. whorls, 'with a 

 carinate acute margin ; B. umbilicate, the' 

 whorls rounded; C. rounded, imperfo- 

 rate ; D. tapering ; E. ovate, im perforate. 

 Of the species, we shall notice H. cornea, 

 the shell of which above is umbilicate, 

 flat, blackish, with four round whorls. It 

 is found in Europe, and on the coast of 

 Coromandel, from a single line to an inch 

 in diameter ; shell chesnut brown, rufous, 

 whitish, yellowish, or blueish, polished 

 and very fine striate transversely; 

 whorls, four or five, rarely turned contra- 

 ry ; the inhabitant is black, with dirty- 

 grey tentacula, and produces a scarlet, 

 but not vry durable dye. H. pomatia, a 

 snail with five spires remarkably ventri- 

 cose, slightly umbilicated, fasciated with a 

 lighter and deeper brown : this is found 

 in the woods of the southern counties of 

 England ; it is said to have been introduc- 

 ed by Sir Kenelm Uigby, for medical pur- 

 poses. These art- confined to the south- 

 ern counties, attempts having been made, 

 but without success, to bring them into 

 Northamptonshire. This snail is used in 

 many parts of Europe as food, particular- 

 ly at Rome during the weeks of Lent: 

 here they are fattened, and grow to a very 

 large size. It is oviparous, very tenacious 

 of life, and, towards winter, covers its 

 aperture with a calcareous lid. H. horten- 

 sis, garden-snail, shell imperforate, globu- 

 lar, pale, with broad interrupted brown 

 bands : this species inhabits the garden 

 and orchard in most parts of Europe; it 

 abounds with a viscid slimy juice, which 

 it readily gives out by boiling in milk and 

 water, so as to render them thick and 

 glutinous, and the compound, especially 

 with milk, is reckoned efficacious in con- 

 sumptive cases. Snails are very destruc- 

 tive to wall-fruit : lime and ashes sprin- 

 kled on the ground will keep them away, 

 and destroy the young brood. Fruit, al- 

 ready bitten, should not be taken off the 

 tree, for they will not touch the other, till 

 they have wholly jeaten this, if left for 

 them. The eyes of snails are lodged in 

 their horns, one at the end of ench horn, 

 which they can retract with pleasure. The 



