ELATER BEETLE 



to the strain it produces. It is 

 generally assumed that the strain is 

 small, as the elasticity of a s-olid has 

 a definite limit (the "elastic limit" ), 

 and when the strain exceeds this 

 limit it produces a permanent 

 deformation or actual fracture. 



A simple example of Hooke's 

 Law is afforded by a steel wire 

 stretched under the tension of a 

 weight suspended from it. Hence 

 the weight is the stress, the longi- 

 tudinal extension of the wire the 

 strain, and it is found that for 

 comparatively small strains the 

 extension is proportional to the 

 weight. Moreover, if wires of the 

 same material, but of different 

 lengths and thicknesses, are com- 

 pared, the ratio of stress to strain 

 is still constant, if each is measured 

 on a suitable scale. It is found that 

 for any given material, such as steel, 

 the ratio of stress to strain is con- 

 stant, and this constant number is 

 called "Young's modulus" for the 

 material. For steel wire it is 

 about 13,000 tons to the square 

 inch, and from this value it is easy 

 to calculate by simple proportion 

 the longitudinal extension of a 

 steel wire of any given length and 

 cross- section, when stretched by 

 a known weight. 



In this case the wire suffers a 

 change in volume as well as in 

 form ; the longitudinal expansion 

 is accompanied by a slight lateral 

 contraction, but the volume of 

 the wire is on the whole increased. 

 A strain in which there is pure 

 change of form with no change of 

 volume is known as a " simple 

 shear " ; it may be illustrated by 

 twisting a wire. Here, again, for 

 small twists the ratio of the " shear- 

 ing stress " to the " shearing 

 strain " is constant, this constant 

 being known as the " rigidity." 

 When a solid or a liquid is com- 

 pressed, the ratio of the compress- 

 ing force per unit of surface area 

 (stress) to the proportionate dimi- 

 nution hi volume (strain) gives 

 another constant, the " volume 

 elasticity," or " bulk modulus." 



The theory of elasticity is of 

 great importance to the engineer 

 who has to deal in every kind 

 of structure and machine with 

 material in a state of stress, and 

 consequently to 



"" ~*jjy~~ -1] some extent in 

 "\H^B_ 1 a state of 



/JHJL ^strain. See 

 / flY-, j Ma terials, 

 sHif) i Strength of. 



I Elater Bee* 



i tie (Gr. elater, 

 driver). Group 

 -^ of beetles, also 



*<;?"? called click 



oeeue /u AA fi Aa rpu ft 



the genus beetles. Ine 



Elater destructive 



2836 



wire-worm is the larva of one of 

 these beetles; and the fire-fly of 

 the W. Indies belongs to the same 

 group. See Beetle; Click Beetle. 

 Elatinaceae. Natural order of 

 herbs and small shrubs, distributed 

 generally over the globe. They are 



Elatinaceae. 1. Flowering branch, 

 magnified. 2. Diagram of a dimer- 

 ous flower. 3. A flower, more mag- 

 nified. 4. A magnified stamen, 

 outside and inside view. 5. Pistil, 

 magnified. 6. Pistil, vertical section, 

 snowing placentae. 7. Magnified 

 seed. 8. Transverse section of seed 



mostly small annuals, growing in 

 marshes, with opposite or whorled 

 leaves. The minute flowers have 

 two to five sepals and a like num- 

 ber of petals, and the fruit is a 

 membranous capsule, containing 

 many seeds. Some of the plants are 

 acrid, being known as waterpeppers. 

 Elba (Gr. Aithalia, Lat. Ilva). 

 Island of the Mediterranean, be- 

 longing to Italy and included in 

 the prov. of Leghorn. It lies 6 m. 

 S.W. of Piombino, the nearest 



ELBE 



Marina are among the chief villages. 

 In 453 B.C. Elba was laid waste by 

 the Syracusans. Pop. 30,450. 



Elbasan. Town of Albania. 

 On the Skumbi, about 65 m. W. 

 of Monastir, it is one of the few 

 important towns of the country, 

 and is the seat of a Greek bishop. 

 It has hot sulphur springs. During 

 the Great War it was the head- 

 quarters for a short time of a gov- 

 ernment formed by Essad Pasha, 

 the Albanian notable who sided 

 with the Allies. After their con- 

 quest of Montenegro and N. 

 Albania, the Austrians occupied it 

 in 1916, but it was recovered by 

 the Allies in Oct, 1918. Pop.13,000. 



Elbe (anc. Albis). River of 

 North -Central Europe. It rises in a 

 number of streams which unite at 

 the foot of the Schneekoppe, a lofty 

 summit of the Giant Mts. (Riesen- 

 gebirge), which extend along the 

 N.E. boundary of Bohemia. From 

 this mountain, at an alt. of 4,500 ft., 

 it flows S. and W. to Melnik, the 

 head of navigation, 21 m. N. of 

 Prague. It penetrates the Mittel- 

 gebirge and the Erzgebirge, waters 

 Saxony, and pursues a N.W. trend 

 to fall into the North Sea, near Cux- 

 haven, through an estuary of 70 m. 

 between Holstein and Hanover. 



At its mouth it is nearly 14 m. in 

 width, its length is 725 m., and its 

 drainage area about 57,000 sq. m. 

 It is navigable by small steamers 

 for more than 500 m., as far as its 

 junction with the Moldau at Melnik. 

 The tide is perceptible as far as 

 Geesthacht, about 110 m. from 

 its mouth. Besides the Moldau, 

 the chief of its many tributaries are 



Elba. Fortress and lighthouse of Porto F err a jo, the capital 



point on the mainland, and is 19 m. 

 long by 6 m. broad, with an area 

 of about 90 sq. m. It is wholly 

 mountainous, rising to 3,350 ft. in 

 Monte Capanne, with fertile valleys. 

 The produce of the island includes 

 iron, which has been worked from 

 antiquity, salt, granite, marble, 

 chalk, and wine. Many of its fisher- 

 folk are engaged in the tunny and 

 sardine fisheries. 



The capital is Porto Ferrajo (9.1;. ) 

 on the N. coast, the residence of 

 Napoleon while in exile, May 5, 

 1814, to Feb. 26, 1815. He had 

 also a villa a few miles S.W. of the 

 town and a country house on Monte 

 Capanne. Porto Longone and Bio 



the Havel, Saale, Eger, and Mulde. 

 The Elbe is linked up by a series 

 of canals with the Oder, the Spree, 

 and the Trave, the latter, opened in 

 1900, connecting Liibeck with 

 Lauenburg. Hamburg, Magdeburg, 

 Meissen, Aussig, Dresden, Torgau, 

 and Wittenberg are important cities 

 on its banks. 



There is an enormous traffic 

 along the Elbe, principally by 

 barges, which are assisted by an 

 ingeniously contrived towing chain. 

 Immense quantities of timber are 

 floated downstream from the 

 forests of Bohemia. Plenty of fish 

 are to be obtained, including stur- 

 geon, salmon, pike, and shad. 



