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 f-. 
6 X 6 = 36 
36 
1296 
20000 
12 X 12 = 144 
50 = length 
7200 
3000 = force 
25920000 25920000)21600000(0.83 = deflection, 
or nearly iths of an inch. And as the deflection will be directly as the force, 
a weight or force of 300lbs. would produce a deflection of x^th of an inch. 
Table of the Modulus of Torsion. 
Species of Wood. 
Specific 
gravity. 
Modulus of 
Torsion. 
Pounds. 
Observations. 
Acacia 
.795 
28293 
Not quite dry. 
Alder 
.55 
16221 
Cross-grained. 
Apple 
.726 
20397 
Ash 
20300 
Of my own planting. 
Ash, mountain . . . 
.449 
13933 
Beech 
21243 
Birch 
17250 
Box 
.99 
30000 
Old, and very dry. 
Brazil wood .... 
1.05 
37800 
Old, and very dry. 
Cane 
21500 
Influenced by the hard surface. 
Cedar, scented . . . 
12500 
Cherry 
•71 
22800 
Chesnut, sweet . . . 
18360 
Chesnut, horse . . . 
.615 
22205 
* If the transverse section of the prism or shaft be not a square, but a parallelogram, let b = 
the breadth, and d the depth : the deflection will be obtained by the following formula : 
(d-f 6)lr f W _ * 
2 b d 3 T ~ * 
f If the measure of torsion should be required in degrees (A) 
let p = 57.29578 then - 
= A 
or let — = t then = A 
( dr t 
thus for wrought iron and steel r ^ - A - = A 
cast iron 
rlw 
16600 d* 
31000 d 4 
= A 
MDCCCXXIX. 
s 
