MR. BEVAN ON THE MODULUS OF TORSION. 



129 



the end of the radius r. As an example, let there be a square* shaft of English oak 

 50 inches long and 6 inches by 6 inches, subject to a strain of 3000lbs. at the cir- 

 cumference of a wheel of 2 feet in diameter, or having a leverage of 12 inches-)-. 

 6 X 6 = 36 12 X 12= 144 



36 60 = length 



1296 

 20000 



7200 



3000 = force 



25920000 25920000)21600000(0.83 = deflection, 



or nearly |ths of an inch. And as the deflection will be directly as the force j 

 a weight or force of 300lbs. would produce a deflection of xVth of an inch. 



Table of the Modulus of Torsion. 



Species of Wood. 



Specific 

 gravity. 



Modulus of 

 Torsion. 

 Founds. 



Observations. 



Acacia . . . 

 Alder . . . 

 Apple . . . 

 Ash. . . _. 

 Ash, mountain 

 Beech . . . 

 Birch . . . 

 Box. . . . 

 Brazil wood . 

 Cane . . . 

 Cedar, scented 

 Cherry . . . 

 Chesnut, sweet 

 Chesnut, horse 



.795 



.55 



.726 



.449 



.99 

 1.05 



•71 

 .615 



28293 

 16221 

 20397 

 20300 

 13933 

 21243 

 17250 

 30000 

 37800 

 21500 

 12500 

 22800 

 18360 

 22205 



Not quite dry. 

 Cross-grained. 



Of my own planting. 



Old, and very dry. 

 Old, and very dry. 

 Influenced by the hard surface. 



* If the transverse section of the prism or shaft be not a square, but a parallelogram, let h = 

 the breadth, and d the depth : the deflection will be obtained by the following formula : 



(d + t)<r'W _ J 



2bd'T 



f If the measure of torsion should be required in degrees (A) 



let p = 57.29578 then L^ 



= A 



T 

 or let — : 



t then -^ = A 



thus for wrought iron and steel 



rlw 



cast iron 



MDCCCXXIX. 



16600d« 

 S 



rlw 



SlOOOrf* 



= A 



= A 



