258 
MAJOR A. E. OXLEY ON THE INFLUENCE OF MOLECULAR 
molecules orientate themselves during crystallization under the influence of the local 
forcives which are characteristic of the molecular configuration. The influence of these 
local forcives will produce in the crystalline medium a distribution of internal stress 
which will in general be different across different planes, and in this way the planes 
of cleavage can he defined. In the dmection where the stress is greatest, we should 
expect the elastic properties of the crystal to he abnormally high, comparable in fact 
with the elastic properties of steel. 
In other directions we should expect the elastic properties to be less pronounced, 
and indeed the shearing of crystals, merely by the insertion of a knife blade and the 
application of small pressure parallel to a plane of cleavage, is evidence of this. 
The following values of Young’s Modulus of Rigidity for various ferro-magnetic, 
paramagnetic, and diamagnetic media show that the power to resist distortion is of 
the same order whatever the magnetic nature of the crystalline medium. 
Substance. ' 
Magnetic nature. 
Young’s modulus 
(dynes per square 
centimetre). 
Rigidity (dynes per 
square centimetre). 
Iron (0 • 1 per cent, carbon) 
ferro-magnetic 
2-13 X 1012 
8-3 X 1011 (calc.) 
Steel (1 per cent, carbon) . 
>1 
2-09 X 1012 
8-1 X 1011 
Nickel. 
JJ 
2-02 X 1012 
7'7 X 1011 (calc.) 
Aluminium. 
paramagnetic 
7-05 X 1011 
2-67 X 1011 
Tin. 
,5-43 X 1011 
2-0 X 1011 (calc.) 
Glass . 
(sometimes diamagnetic) 
6-5-7-8 X 1011 
2-6 xlOii 
Jc J 
Platinum. 
paramagnetic 
l-68x 1012 
6-1 X 1011 
Lead. 
diamagnetic 
1-62 X 1011 
O'56 X 1011 (calc.) 
Zinc. 
1-25 X 1012 
5 X 1011 
Copper . 
1-23 X 1012 
4-55 X 1011 
Silver. 
7-9 xlOii 
2-87 X 1011 
Gold. 
8-0 X 1011 
2-77 X 1011 
Bismuth. 
n 
3-19x 1011 
1-2 X 1011 (calc.) 
Quartz (fibre). 
5) 
5-18 X 1011 
3-0 xlOii 
Principal Young’s 
Principal rigidity 
moduli (dynes per 
(dynes per square 
scpiare centimetre). 
centimetre). 
Quartz (crystalline) . . . 
diamagnetic 
1-OOx 1012 
5-7 X 1011 
Beryl. 
paramagnetic 
2-06 X 1012 1 
L 
6-54 X 10111 
2-25 X 1012 J 
9-6 xlOiiJ 
Topaz . 
diamagnetic 
2-25 X 10120 
— 
t - 
1 
) 
2 • 83 X 1012 
— 
2-60x 1012 
— 
Rock salt. 
0-41 X 1012 
1-27 X 1011 
i 
Potassium chloride . . . 
0-36 X 1012 
0-64x 1011 
Fluor spar. 
n 
1 ■ 44 X 1012 
3-4 xlOii 
1 
Pyrites. 
— 
3-46 X 1012 
1 
10-5 xlOii 
* Kaye and Laby, ‘ Physical and Chemical Constants,’ p. 27, 1918. 
t A. E. H. Love, “The Mathematical Theory of Elasticity,” ‘ Camb. Univ. Press,’ p. 160. In the 
cases of beryl and topaz the different values correspond to bars whose lengths are in the directions of the 
different axes of symmetry. 
