L A 



Hence we may find the weights which columns of given materials 

 will support. Thus, if in fir-wood the modulus E be 10,000,000 feet, a 

 bar, an inch square, and 10 feet long-, may begin to bend, when 



F = .8225 X -~f- X 10,000,000 = 571 feet. 



3. Elasticity of Torsion. 



1. Let/and/' be the forces necessary to twist a metallic thread, from 

 the position in which it would naturally hang, through the ,/s. 8 and fr ; 

 then if 6 and 6' be very small, 



/ _ * 

 J> ~ p- 



On this principle depends the Torsion Balance of Coulomb, which has 

 been employed for the purpose of measuring very small repulsive and 

 attractive forces. In some cases the instrument was constructed with 

 so much delicacy, that each degree of torsion required a force of only 



Height of the Modulus of Elasticity in thousands of feet ( Encyclop. 

 Brit. Supplem.) 



Iron and steel ~~~~~ ~~~~* 10,000 Fir wood ,~~~~~ 10,000 



Copper *, 5,700 Elm 8,000 



Brass 5,000 Beech 8,000 



Silver ww ~ w ~ w , ,, w 3,240 Oak *~~~ ~~ , * 5,060 



Tin^^ <w ~ ww ~, w ,~ w 2,250 Box . w ~.,,~~ 5,050 



Crown glass w ^^^^ w 9,800 Ice ~ w > w ~~ ^^^^^ ,850 



The following Table is the result of experiments by Mr. Rennie, pub- 

 lished in the first part of the Phil. Trans, for 1818. 



Mr. Rennie found a cubical inch of the following bodies crushed by 

 the following weights : 



Ibs. av. 



^ WWJ ^r WW ^ JJWWWWJ ^r W r WJ -x J u- JJJ - JW x Ww r J ^nn 1284 



American Pine _ 1606 



White Deal ,_ , 1928 



English Oak ^ 5860 



Cube* of 1% inch. 



Sp. gr, 

 1127 



Derby Grit- 



Portland *. 



101 



