Page:Popular Science Monthly Volume 44.djvu/265

Rh The final objection to his theory was one of Rey's own suggestion: Why does not earth go on increasing in weight indefinitely? Because "the thickened air attaches itself to it and continues to adhere to the most minute of its particles, so that its weight goes on increasing from the beginning to the end; but when it is all enveloped in air it can not take any more." He concludes then, and terminates his treatise by declaring with pride that he has found the real way of the truth, breaking the road for his successors, and advising them not to go astray from it.

This is the summary of the works of Jean Rey. A skillful experimenter, he knew how to use the balance, and it was the balance that suggested to him the result of his experiments. His book is a brief one. A single principal experiment is described, a single object is pursued in it. But he made two great advances in science. He discovered the weight of the air, being the first to publish that hypothesis, and verified it by experiments in chemistry and physics. The increase of the weight of lead and tin on calcination had been noticed for a long time by the alchemists, and even Galen knew of it. But nobody before Rey found that the cause of that increase in weight came from the air from that thickened and heavy air. It was certainly a remarkable achievement to announce such a fact at a time when chemistry had made so little advance. No gas was yet known; and it was not till about 1719 that a misunderstood man of science, Mortrel d'Élément, found means to decant air through water into bottles, and taught in a public lecture in Paris "how to make air visible and perceptible enough to measure it in pints or in whatever quantity you will." It was not his fault, therefore, that he did not advance further.—Translated for The Popular Science Monthly from the Revue Scientifique.

a possible solution, or working hypothesis, of the reason of the migration of birds, Canon Tristram suggests: "Instinct in mammals and birds attracts them to the place of their nativity. When the increasing cold of the northern regions, in which they all had their origin, drove the mammals southward, they could not retrace their steps, because the increasing polar sea, as the arctic continent sank, barred their way. The birds reluctantly left their homes as winter came on and followed the supply of food. But as the season in their new residence became hotter in summer, they instinctively returned to their birthplaces, and there reared their young, retiring with them when the recurring winter impelled them to seek a warmer climate. Those species which, unfitted for a greater amount of heat by their more protracted sojourn in the northern regions, persisted in revisiting their ancestral homes, or getting as near to them as they could, retained a capacity for enjoying a temperate climate, which, very gradually, was lost by the species which settled down more permanently in their new quarters, and thus a law of migration became established on the one side, and sedentary habits on the other."