438. Water furnishes an eminent example of this special solidifying power. It may be cooled ten degrees and more below its freezing point without freezing. But this is not possible if the smallest fragment of ice be floating in the water. It then freezes accurately at 32° Fahr., depositing itself, however, not upon the sides of the containing vessel, but _upon the ice_. Faraday observed in a freezing apparatus thin crystals of ice growing in ice-cold water to a length of six, eight, or ten inches, at a temperature incompetent to produce their deposition upon the sides of the containing vessel. 439. And now we are prepared for Faraday's view of regelation. When the surfaces of two pieces of ice, covered with a film of the water of liquefaction, are brought together, the covering film is transferred from the surface to the centre of the ice, where the point of liquefaction, as before shown, is higher than at the surface. The special solidifying power of ice upon water is now brought into play _on both sides of the film_. Under these circumstances, Faraday held that the film would congeal, and freeze the two surfaces together. 440. The lowering of the freezing point by pressure amounts to no more than one-seventieth of a degree Fahrenheit for a whole atmosphere. Considering the infinitesimal fraction of this pressure which is brought into play in some cases of regelation, Faraday thought its effect insensible. He suspended pieces of ice, and brought them into contact without sensible pressure, still they froze together. Professor James Thomson, however, considered that even the capillary attraction exerted between two such masses would be sufficient to produce regelation. You may make the following experiments, in further illustration of this subject:-- 441. Place a small piece of ice in water, and press it underneath the surface by a second piece. The submerged piece may be so small as to render the pressure infinitesimal; still it will freeze to the under surface of the superior piece. 442. Place two pieces of ice in a basin of warm water, and allow them to come together; they freeze together when they touch. The parts surrounding the place of contact melt away, but the pieces continue for a time united by a narrow bridge of ice. The bridge finally melts, and the pieces for a moment are separated. But capillary attraction immediately draws them together, and regelation sets in once more. A new bridge is formed, which in its turn is dissolved, the separated pieces again closing up. A kind of pulsation is thus established between the two pieces of ice. They touch, they freeze, a bridge is formed and melted; and thus the rhythmic action continues until the ice disappears.