The Mangaians of the South Pacific told the earlier missionaries of a feat of one of their heroes which at first was unaccountable. This demigod, Maui, a sort of Pacific Hercules, raised the sky to its present position. Not getting it high enough to suit him, he put his head between the legs of his old father Ru, and heaved him and the half-raised sky up together. Ru stuck fast among the stars, and Maui left him there till his body dropped to pieces and his bones fell over the ground below. To prove the truth of their story they brought the missionaries bits of pumice, which they said were the bones of Ru. Singularly enough the white porous stone looked much like bone. The myth had been invented by the simple folk to explain the origin of pumice. The ashes, or volcanic dust, is excessively minute, and in consequence readily penetrate crevices that are hardly visible. Professor Bonney, examining dust thrown out by Cotopaxi, has calculated that it would require from four thousand to twenty-five thousand particles to make up a grain in weight. The substance known as tufa is merely volcanic dust or ash upon which rain has fallen while the former was still hot. The resultant paste solidifies into a porous and loosely compacted rock. Why some volcanoes nearly always throw out dust and fragments, while others throw out mere molten streams, was for a time not clearly understood. Some suggested the dust was the result of the continual collision of fragments as they rose and fell, and hence would increase in quantity as the eruption continued. This clearly would not meet the case of volcanoes which, without showing any previous signs of activity, burst into action with tremendous volumes of dust. It was at length noticed that dust and fragments always were accompanied by tremendous explosions; while eruptions of melted lava were far more quiet, shocks being few and the explosions insignificant as compared with the former. This gave a clue to the mystery. Many liquids and solids have the power of absorbing vast quantities of gas. Under pressure their absorbing powers may be vastly increased. Sometimes the property appears only at high temperatures. Silver when melted absorbs twenty-two times its volume of oxygen. If suddenly cooled the oxygen is given off with a rapidity verging on explosion. This is called the “spitting” of silver. Tiny cones and melted streams appear on the cooled surface--volcanoes in miniature. The same property belongs to the oxide of lead, and some other metals.