The nineteenth century closed with many important problems in electrical science unsolved. What great or far-reaching discoveries are yet in store, who can tell? What valuable practical developments are to come, who can predict? The electrical progress has been great—very great—but after all only a part of that grander advance in so many other fields. The hands of man are strengthened by the control of mighty forces. His electric lines traverse the mountain passes as well as the plains. His electric railway scales the Jungfrau. But he still spends his best effort, and has always done so, in the construction and equipment of his engines of destruction, and now exhausts the mines of the world of valuable metals, for ships of war, whose ultimate goal is the bottom of the sea. In this also electricity is made to play an increasingly important part. It trains the guns, loads them, fires them. It works the signals and the search-lights. It ventilates the ship, blows the fires, and lights the dark spaces. Perhaps all this is necessary now, and, if so, well. But if a fraction of the vast expenditure entailed were turned to the encouragement of advance in the arts and employments of peace in the twentieth century, can it be doubted that, at the close, the nineteenth century might come to be regarded, in spite of its achievements, as a rather wasteful, semi-barbarous transition period? ELIHU THOMSON. PHYSICS On January 7, 1610, Galileo, turning his telescope towards Jupiter, was the first to see the beautiful system of that planet in which the universe is epitomized. He had already studied the variegated surface of the moon, and he had seen the spots upon the sun. A little later, in spite of the feeble power of his instrument, he had discovered that the sun rotates upon an axis, and something of the wonderful nature of the planet Saturn had been revealed to him. The overwhelming evidence thus afforded of the truth of the hypothesis of Copernicus made him its chief exponent. The time had come for man to know, as he had never known or even dreamed before, his true relation to the universe of which he was so insignificant a part. In a single year nearly all of these capital discoveries were made. It was truly an era of intellectual expansion; never before and never since has man’s intellectual horizon enlarged with such enormous rapidity. One needs little imagination to share with this ardent philosopher the enthusiasm of the moment when, because some, fearing the evidence of their senses, refused to look through the slender tube, he wrote to Kepler: “Oh, my dear Kepler, how I wish we could have one hearty laugh together!... Why are you not here? What shouts of laughter we should have at this glorious folly!”