90 Mr. H. H. Howorth on 



will relieve the pressure where the compression and lique- 

 faction of the ice takes place ; on the removal of the 

 pressure the water will be frozen by the cold liberated, as 

 already mentioned ; the water thus freezing in a new 

 position will cause a change of form, and a plastic yielding 

 of the mass of the ice. The yielding of one part leaves 

 another part free from pressure, and that acts in a similar 

 manner, and on the whole a continual succession goes on of 

 pressures beingapplied to particular parts, liquefaction in those 

 parts — dispersion of the water so produced, in such directions 

 as will relieve its pressure, and recongelation by the cold 

 previously evolved, of the water on its being relieved from 

 this pressure. The parts recongealed after having been 

 melted must in turn, through the yielding of other parts,, 

 receive pressures from the applied forces, thereby to be 

 again liquefied and to enter again on a similar cycle of 

 operation." 



Professor Thomson adds a note to the effect that the 

 case is not limited to ice originally porous. If ice be kept 

 at or above 0° centigrade, then as soon as pressure is applied 

 to it, pores occupied by liquid water must immediately be 

 formed in the compressed parts, and no part of the ice,, 

 however solid, can resist being permeated by the water 

 squeezed against it, which by its pressure must cause 

 melting to set in, thereby reducing it to a porous condition 

 {Phil. Mag., 4th sen, XIV. 549 — 550). 



The objections to this theory, countenanced as it has 

 been by some great names, including Helmholtz, are in- 

 superable. Thus, as Mr. Brown urges, "its advocates 

 hardly seem to consider how very small the lowering 

 of the freezing point is for any ordinary pressure. It 

 is only '0075 per atmosphere. In other words, it will 

 require a pressure of 2,000 lbs. per square inch to liquify 

 ice at 31° instead of 32°. This is equivalent to the weight 

 of a column of ice about 5,000 feet high. It is needless 



