There are at least two of the low-temperature phenomena, however, that seem a little less puzzling--the facts, namely, that cohesion and rigidity of structure are increased when a substance is cooled and that chemical activity is very greatly reduced, in fact almost abolished. This is quite what one would expect _a priori_--though no wise man would dwell on his expectation in advance of the experiments--since the whole question of liquids and solids _versus_ gases appears to be simply a contest between cohesive forces that are tending to draw the molecules together and the heat vibration which is tending to throw them apart. As a substance changes from gas to liquid, and from liquid to solid, contracting meantime, simply through the lessening of the heat vibrations of its molecules, we might naturally expect that the solid would become more and more tenacious in structure as its molecules came closer and closer together, and at the same time became less and less active, as happens when the solid is further cooled. And for once experiment justifies the expectation. Professor De-war found that the breaking stress of an iron wire is more than doubled when the wire is cooled to the temperature of liquid air, and all other metals are largely strengthened, though none other to quite the same degree. He found that a spiral spring of fusible metal, which at ordinary temperature was quickly drawn out into a straight wire by a weight of one ounce, would, when cooled to -182 deg, support a weight of two pounds, and would vibrate like a steel spring so long as it was cool. A bell of fusible metal has a distinct metallic ring at this low temperature; and balls of iron, tin, lead, or ivory cooled to -182 deg and dropped from a height, "in all cases have the rebound greatly increased. The flattened surface of the lead is only one-third what it would be at ordinary temperature." "These conditions are due solely to the cooling, and persist only while the low temperature lasts."