degrees and its great expansion in congelation, these disastrous consequences are prevented. Our lakes are cooled even in winter only to thirty-nine and a half degrees; below this temperature the colder water is lighter and remains upon the surface; ice floats upon the surface. The top becomes ice, but the great mass of the water remains at thirty-nine degrees, and the inhabitants of the waters live on unharmed. Spring comes, and the ice, being upon the surface, is soon melted, and the unbound waves begin again to ripple forth their unconscious joy." "Do you look upon this irregular expansion and contraction of water," asked Mr. Hume, "as a real exception to the rule that heat expands bodies?" "Not at all. In freezing, a new force comes in and asserts itself--the force of crystallization; or, more exactly, as the force of heat diminishes the force of crystallization becomes predominant, and throws the atoms into new positions and new relationships. To this new arrangement of atoms is due the expansion in freezing. Ice contracts and expands by cold and heat the same as any other solid. The attraction of crystallization begins, doubtless, to throw the atoms into their new and crystalline arrangement at the temperature of thirty-nine and a half degrees. "We must remember that the heat which is set free in the condensation of vapor and in the freezing of water is absorbed in the formation of vapor and the melting of water. As much heat is taken from summer as is conferred upon winter. The summer is cooled as much as winter is warmed. The formation of vapor is a cooling process. Water is prevented from rising above the boiling point by the formation of vapor. Perspiration cools us by the evaporation to which it gives rise from the whole surface of our bodies. And the higher the temperature, the more rapid the evaporation, and the more vigorous the cooling process.