[A] 'Occ. Pap.,' p. 224.
[B] 'Phil. Trans.,' 1846, p. 137, and 'Occ. Pap.,' p. 138.
[C] 'Occ. Pap.,' p. 47.
[D] 'Phil. Mag.,' 1857, vol. xiv., p. 241.
THOMSON'S THEORY.
(21.)
In the 'Transactions' of the Royal Society of Edinburgh for 1849 is published a very interesting paper by Prof. James Thomson of Queen's College, Belfast, wherein he deduces, as a consequence of a principle announced by the French philosopher Carnot, that water, when subjected to pressure, requires a greater cold to freeze it than when the pressure is removed. He inferred that the lowering of the freezing point for every atmosphere of pressure amounted to .0075 of a degree Centigrade. This deduction was afterwards submitted to the test of experiment by his distinguished brother Prof. Wm. Thomson, and proved correct. On the fact thus established is founded Mr. James Thomson's theory of the "Plasticity of Ice as manifested in Glaciers."
STATEMENT OF THEORY.
The theory is this:—Certain portions of the glacier are supposed first to be subjected to pressure. This pressure liquefies the ice, the water thus produced being squeezed through the glacier in the direction in which it can most easily escape. But cold has been evolved by the act of liquefaction, and, when the water has been relieved from the pressure, it freezes in a new position. The pressure being thus abolished at the place where it was first applied, new portions of the ice are subjected to the force; these in their turn liquefy, the water is dispersed as before, and re-frozen in some other place. To the succession of processes here assumed Mr. Thomson ascribes the changes of form observed in glaciers.