ELASTICITY 



101 



Two descriptions of elastic bitumen were analysed by M. Honry fils (' Ann. dcs 

 Mines '). He'statcs tlio English to have been in brown masses, slightly translucid, of 

 a greenish colour, soft, elastic, burning with a white flame, and giving off a bitu- 

 minous odour, and of specific gravity 0"9 to T23, and obtained from Derbyshire. 



The French elastic bitumen generally resembled the English, excepting that it was 

 opaque, and floated on water. It was discovered at the coal-mines of Montrelais. 



English French 



Carbon .... 0'5225 . . 0-5826 

 Hydrogen .... 0-0742 . . 0-0489 



Nitrogen 

 Oxygen 



0-0015 

 0-4011 



1-0000 



0-0010 

 0-3675 



1-0000 



Elastic bitumen is found in soft, flexible masses at Castleton in Derbyshire. See 

 BITUMEN. 



ELASTICITY. The property which bodies possess of occupying, and tending 

 to occupy, portions of space of determinate volume, or determinate volume and figure, 

 at given pressures and temperatures, and which, in a homogeneous body, manifests 

 itself equally in every part of appreciable magnitude (Nickel). The examination of 

 this important subject in Kinetics does not belong to this work. A few remarks, and 

 some explanations, only are necessary. 



Elastic Pressure is the force exerted between two bodies at their surface of contact. 



Compression is measured by the diminution of volume which the compressible 

 (elastic) body undergoes. 



The Modulus or Coefficient of Elasticity of a liquid is the ratio of a pressure applied 

 to, and exerted by, the liquid to the accompanying compression, and is therefore the 

 reciprocal of the compressibility. The quantity to which the term Modulus of 

 Elasticity was first applied by Dr. Young, is the reciprocal of the extensibility or 

 longitudinal pliability. (See the Edinburgh Transactions, and those of the Royal 

 Society, for the papers of Barlow, Maxwell, and Rankine, and the British Association 

 Eeports for those of Fairbairn, Hodgkinson, &c.) 



Various tables, showing the elasticity of metals, glass, &c., have been constructed, 

 and will be found in treatises on mechanics. The following notices of the mecha- 

 nical properties of woods may prove of considerable interest. The experiments were 

 by Chevandier and "Wertheim. 



Rods of square section 10 mm. in thickness and 2 m. in length were prepared, being 

 cut in the direction of the fibres, and the velocity of sound in them was determined by 

 the longitudinal vibrations, their elasticity from their increase in length, and their co- 

 hesion by loading them to the point of rupture. Small rods were cut in planes per- 

 pendicular to the fibre grain (in directions radial and tangential to the rings of growth) 

 and their elasticity and sound velocity were measured by the lateral vibrations. It was 



