ELL 



EMA 



Logic, a syllogism by which the adversary 

 is forced to contradict himself. The 

 ignoratio elenchi, commonly called the 

 fallacy of irrelevant conclusion, is a 

 sophism which consists in proving some- 

 thing irrelevant, and therefore, though 

 it may be perfectly true, it does not de- 

 termine the question. The latent fallacy 

 is best exposed by showing that both 

 propositions may be equally true. 



ELEVATING CAUSES. A term ap- 

 plied in Geology to those causes which 

 refer to the operation of volcanoes, earth- 

 quakes, and gradually elevating forces. 

 As degrading causes are chiefly owing to 

 water, so elevating causes are chiefly 

 owing to fire, and are, therefore, some- 

 times comprehended under the term 

 igneous agency. 



ELEVA'TION {elevo, to lift up). In 

 Astronomy, the altitude or angular 

 height of a celestial body above the 

 horizon. The elevation of the pole is the 

 arc of the meridian intercepted between 

 the pole and the horizon. 



ELIMINATION {elimino, to put out). 

 The algebraical operation of reducing a 

 number of equations, containing certain 

 letters, to a smaller number, in which 

 one or more of the letters shall not occur. 

 To eliminate a quantity is, therefore, to 

 cause that quantity to disappear from an 

 equation. 



ELIQUA'TION {eliquo, to clarify). The 

 separation of a more fusible from a less 

 fusible substance, by applying a degree 

 of heat sufficient to fuse the former, but 

 not the latter. 



ELI'SION {elisio, a cutting off"). In 

 Grammar, the cutting off" a vowel at the 

 end of a word, for the sake of euphony 

 or of metre. 



ELIXIR {elikscir, Arab., an essence, 

 or pure mass without any dregs), A 

 term formerly applied to compound tinc- 

 tures, and, by the alchemists, to various 

 solutions in the art of transmutation. 



ELLAGIC ACID (from the word galle, 

 read backward). An acid which is ob- 

 tained from galls, in the process for 

 making gallic acid. 



ELLIPSE {€\\et\lfii, a defect). A sec- 

 tion of a right cone by a plane oblique to 

 its base, but which does not meet it. It 

 is named fr9m its plane forming with the 

 base of the cone a less angle than that of 

 the parabola. To describe it, fix a cir- 

 cular thread by two points, and, keeping 

 it at full stretch with the point of a pen- 

 cil, carry the pencil all round : the two 

 fixed points are the foci of the ellipse, 

 119 



and its eccentricity is its distance from 

 the centre to the foci. 



Ellipse, axes of. By generalizing these 

 directions, we learn that an ellipse is a 

 plane figure bounded by one curved line, 

 of such a nature that the respective suras 

 of the distances of any two points in it 

 from the two foci, are equal. The line 

 which joins the foci, and terminates both 

 ways in the circumference, is the major 

 axis; the line drawn through the centre 

 at right angles to the major axis, and 

 terminating both ways in the circum- 

 ference, is the minor axis of the ellipse. 



ELLI'PSOID {eWei^i?, an ellipse, 

 e'ldoi, likeness). A term generally ap- 

 plied to a spheroid. The ellipsoid of 

 revolution is the solid generated by the 

 revolution of an ellipse about its lesser 

 axis. 



ELLI'PSOSTO'MATA. A family of 

 Gasteropods, in the arrangement of De 

 Blainville, including all the pectini- 

 branchiate gasteropods of Cuvier, except 

 the genus pleurocerus. 



ELLI'PTIC COMPASSES. An in- 

 strument for describing an ellipse by 

 continued motion. 



ELLIPTPCITY. A term employed 

 in describing the figure of the earth, to 

 denote the deviation of the earth's form 

 from that of a sphere. It means the 

 fraction which the excess of the major 

 axis over the minor axis of an ellipse is 

 of the minor axis itself. 



ELONGATION. An astronomical 

 term for the angular distance between 

 two celestial bodies, as seen from the 

 earth. The term is commonly applied to 

 bodies of the solar system, one of which 

 is generally the sun. Hence, we speak 

 of the distance of two fixed stars, but of 

 the elongation of Mercury from the sun. 



ELUTRIATION {etutrio, to cleanse). 

 The chemical process of washing, by 

 which the lighter earthy parts are sepa- 

 rated from the heavier and metallic. 



ELVAN COURSES. A local desig- 

 nation of the large beds or dykes of gra- 

 nite which frequently occur in the slaty 

 rocks. 



ELYTRA (e'XuTpov, a sheath). The 

 wing sheaths, or upper crustaceous mem- 

 branes, which form the superior wings of 

 Coleopterous insects. They cover the 

 body, and protect the true membranous 

 wings. 



EMA'RGINATE {e, out of, margo, the 

 margin). Having a notch, as if a portion 

 had been cut out of the margin, as the 

 base of most predaceous testacea, not pro* 



