286 
MAJOE A. E. OXLEY ON THE INFLUENCE OF xAIOLECULAE 
experimentally, and point to the importance of the local molecular forcive in magneto¬ 
optic phenomena. It should be noted that the value of the reverse field we have 
taken is that of the intermolecular field. Within the atom the reverse field will 
probably be greater than —6fix 10® gauss. If it is of the order — 5x 10' gauss, the 
above ratios become 320x 10® for iron, 200x 10® for nickel and 700x 10® for cobalt. 
Intra-atomic fields of the order 10® gauss are required by Humphries* to explain the 
pressure shift of spectral lines and by RiTzt in his theory of spectral series (see also 
Part III., p. 100, and supra, p. 273, footnote). 
(8) Summary oe Conclusions. 
(I.) The applications of the local molecular forcive, in diamagnetic, paramagnetic and 
ferro-magnetic media, have in the present research been extended to interpret the 
ultimate tensile strength of crystalline and vitreous media. It has been shown by 
Ewing and Rosenhain that the permanent set which occurs prior to breaking is due 
to slipping along the cleavage planes within the individual crystalline grains. We should 
therefore expect that the material would be fractured when the applied mechanical 
stress is equal to that produced internally by the local molecular forcive. The internal 
stress within the material is shown to be of the order 2x10® dynes per square centimetre 
which is approximately the mean value of the ultimate tensile strengths of crystalline 
and vitreous media (pp. 250-259). 
(II.) As a consequence of this internal stress, the energy per unit volume will be 
2x10® ergs, and this energy, which is over and above that which exists in the fluid 
state, should be a measure of the latent heat of fusion per cubic centimetre. This test 
which was applied in Part III. to test the order of the local forcive, has been extended 
to a variety of organic and inorganic media, including the metals and is found to 
accord with the experimental values to the right order (pp. 253-4). 
(III.) Since the forces under which the molecules vibrate are those to which we 
ascribe the elastic properties of crystalline media, the results obtained are consistent 
with the theory of specific heats developed by Debye, in which the specific heat is 
attributed to purely translational viliration, and it has been shown (Part III.) that, 
near the fusion point, the rotational energy acquired by the molecules will give a 
measurable departure from this theory which is actually observed experimentally. 
As we should expect, it is found that the elastic constants of a variety of ferro¬ 
magnetic, diamagnetic and paramagnetic media are of the same order, several 
diamagnetic and paramagnetic media even surpassing steel in their power to resist 
distortion (pp. 257—259). 
(IV.) Any change of internal pressure will be accompanied by a change of volume 
defined by the compressibility of the medium and dependent as to sign upon 
* ‘ Astrophysical Journal,’ vol. 23, p. 232, 1906; vol. 35, p. 268, 1912. 
t ‘Aim. der Phys.,’ vol. 25, p. 660, 1908. 
