486 Mr. W. Sutherland on the 



But these principles alone would lead us to expect that the 

 melting of ice should be preceded by a stage of general 

 softening, as with sealing-wax, on account of the occurrence 

 of isolated cases of instability before all the molecules got to 

 the unstable point. The sharpness with which the melting 

 of ice occurs seems to me to indicate that we have to do with 

 a phenomenon of molecular resonance. If the collisional 

 forces were removed, and also the intermolecular, then under 

 the chemical forces our triangle ABC would have a natural 

 period of vibration round the equilateral shape of equilibrium. 

 If the period of vibration of each of the atoms A, B, and C, 

 on account of other attractions and collisions, becomes the 

 same as this natural period, then by resonance small de- 

 formations of A B C will be worked up to large enough ones 

 to attain the stage of instability. When some of the ice 

 dissociates into dihydrol, this dissolves the remainder, altering 

 for it both io/D and the period of collisions, thus enabling it 

 to exist. 



The mechanical explanation of the melting of ice as a 

 process of dissociation consists then of two parts : one ac- 

 counting for the occurrence of a position of instability, the 

 other accounting for the sharpness with which all the mole- 

 cules attain this position simultaneously. The complete 

 molecular or mechanical theory of the lowering of the 

 melting-point of ice by pressure must then take account of 

 the change not only of the deformation to/T) with temperature 

 and pressure, but also of the resonance. 



If the surmise is correct that molecular resonance plays 

 an important part in the melting of ice, then the dissociation 

 of trihydrol presents an interesting similarity to that of 

 rarefied ozone, to which I have drawn attention (" The 

 Spontaneous Change of Ozone into Oxygen, and a Remarkable 

 Type of Dissociation, " Phil. Mag. [5] xliii.). As rarefied 

 ozone is gradually compressed, it begins at a pressure of 

 ■14 mm. of mercury to dissociate, because the average fre- 

 quency of collisions between the molecules is the same as 

 some natural frequency of vibration of the constituent atoms, 

 or a simple multiple of it. This frequency must be of about 

 the order 10 8 per second. We can estimate the order of the 

 frequency which is destructive to molecules of trihydrol in 

 the following way : — From the known so-called molecular 

 volumes of hydrogen and oxygen (really their molecular 

 domains) we can infer that the oxygen atom occupies 

 about ^ of the space belonging to H 2 0. Now the linear 

 coefficient of expansion of ice being -000157/3, the linear 

 interspaces between the groups H 2 of ice at 0° centigrade 



