ER Y 



ERI'DANUS. A southern constella- 

 tion, consisting of 84 stars, the principal 

 of which is Achernar. 



ERINACE'AD^. The Urchin or 

 Hedgehog tribe ; a family of insectivor- 

 ous vertebrata, which are remarkable not 

 only for their covering of spines, but for 

 the great development of the muscular 

 envelope of the body immediately beneath 

 the skin. 



E'RINITE. A beautiful emerald-green 

 arseniate of copper, named from its being 

 found in the county of Limerick in Ire- 

 land. 



ERTO'METER (^piov, wool, /jLerpov, a 

 measure). An instrument, invented by 

 Dr. Young, for the purpose of measuring 

 the diameters of minute fibres. 



E'RLAMITE. A new mineral, forming 

 a part of the oldest gneiss formation. 



ERO'SE (erosMjs, gnawed off). Gnawed; 

 having the margin irregularly divided, as 

 if bitten by an animal : a term applied to 

 the margin of certain leaves. 



ERRA'NTES {erro, to wander). A 

 term applied by M. Edwards to an order 

 of the Anellida, which are at once the 

 highest organized and the most locomo- 

 tive. These are the dorsibranchiata of 

 Cuvier, and are commonly known by the 

 names of sea-centipedes, sea-mice, or 

 nereids. 



ERRATIC BLOCKS. A term syno- 

 nymous with boulders, derived from their 

 wide distribution over the surface of the 

 earth. See Boulders. 



ERY'THRO- (epu6>p6f, red). A Greek 

 term employed in composition to denote 

 any pure red colour. It agrees with the 

 ruber of the Latins. 



L Erythric Acid. A red substance pro- 

 duced by the mutual action of the nitric 

 and uric acids. Dr. Prout considers it 

 to be not a peculiar acid, but a com- 

 pound of nitric and purpuric acid and 

 ammonia. 



2. Erythrin. One of a series of sub- 

 stances including erythrilin, erythrin 

 bitter or amarythrin, telerythrin, &c., 

 obtained by Dr. Kane from the Roccella 

 Unctoria. 



3. Erythro-gen (yei/vdo), to produce). 

 A green-coloured substance found in the 

 gall-bladder, in a case of jaundice. It 

 unites with nitrogen, and produces a red 

 compound. 



4. Erythro-phylle (0wX\oi/, a leaf). A 

 term applied by Berzelius to the red 

 colouring matter of leaves and fruits in 

 autumn. 



5. Erythro-stomum (crro/Ma, a mouth). 



128 



EST 



A terra applied by Desvaux io the 

 aggregate fruit, more generally termed 

 etcerio. 



ESCA'RPMENT {escarper, to cut 

 steep). The abrupt face of a ridge of 

 high land, where subjacent strata are 

 observed to '• crop out." 



ESO'CID^ {esox, the pike). The Pike 

 tribe ; a family of Malacopterygious or 

 soft-spined fishes, having the ventral 

 fins placed under the abdomen, and in- 

 cluding most of the voracious fresh- 

 water fishes, as well as several important 

 marine species. They are distinguished 

 by the position of the dorsal opposite to 

 the anal fin, and by the absence of fatty 

 matter in the former. 



ESOTE'RIC (eo-corepiKof, inner). A 

 term applied to the disciples of Pytha- 

 goras, Aristotle, &c., who were scientifi- 

 cally taught, as distinguished from the 

 exoteric, wlio had merely popular views. 

 The term esoteric is sometimes applied to 

 a mysterious doctrine, which was taught 

 only to the more enlightened, and was 

 thus distinguished from the exoteric, or 

 published doctrine. In this sense "eso- 

 teric" is synonymous with acroamatic, 

 or that which is communicated by oral 

 instruction. 



E'SSENCE {essentia, a being). A scho- 

 lastic term denoting the essential perfec- 

 tion of a being, i. e. its entity and attri- 

 butes. It sometimes signifies merely the 

 principal attributes of a being. 



ESSENTIAL DEFINITION. In Lo- 

 gic, a definition which assigns, not the 

 properties or accidents of the thing de- 

 fined, but what are regarded as its essen- 

 tial parts, whether physical or logical. 

 See Definition. 



ESSENTIAL OILS. Oils obtained by 

 distillation from odoriferous vegetable 

 substances. Several of the volatile or 

 essential oils are called essences. 



ESTIVATION {ccstivus, belonging to 

 summer). Prcefioration. A botanical 

 term applied to several modes in which 

 the floral envelopes are folded up in the 

 unexpanded or bud state. It is said 

 to be — 



1. Involute, when the edges are rolled 

 inwardly spirally on each side. 



2. Revolute, when the edges are rolled 

 backwards spirally on each side. 



3. Obvolute, when the margins of one 

 leaf alternately overlap those of the oppo- 

 site leaf. 



4. Convolute, when one leaf is wholly 

 rolled up within another leaf. 



5. Supervolute, when one edge is rolled 



