is that a sphere attracts all outside bodies as if its mass were concentrated at its center.
Thus he reached his goal at last, and after twenty years of work, ranging over many subjects, the key of the universe lies in Newton's hand. Surely, now, he will publish it and proclaim its discovery to the world. Not so; he must first have the joy of undisturbed possession. Also there is much more to be done. The law he has proved is an "open sesame" to wider knowledge. Or, to change the figure, it is as if a mountain climber, who has toiled upward and upward, now stands at last on the topmost height. As he is climbing he thinks that if he can but gain the summit it will be enough—he will be content and rest. The toiling climber does not realize what awaits him at the top, until the whole panorama of plain and mountain, of crag and canyon, bursts upon his astonished sight. With this before him he forgets his toil, forgets to rest and devours the view. So with Newton, having at last mastered the central law upon which the universe swings, he saw the members of the solar system sweeping in orderly grandure through space, he saw this law governing every motion of every satellite and comet, accounting for the nutations and perturbations, which before seemed to make order impossible. He saw it causing the tides with the rising and setting of the sun and moon. All this and more he saw, and we can not wonder that instead of rushing into print, he shut himself up and worked and thought and wrote, and calculated and worked and thought and wrote.
For two years he labored, sleeping little, eating little, always lost in thought. Often, it is said, on rising, he would sit for hours half dressed upon his bedside. Often for days, he would seem oblivious to all external events. The following story well illustrates his abstraction. One day a friend. Dr. Stukely, called and found Newton's solitary dinner ready on the table. After waiting a long while, Dr. Stukely thought to play a joke on Newton, which he proceeded to do by eating his dinner for him. Having done so, he rearranged the table, covering the dishes so that it would not appear that anything had happened. At length Newton appeared, and, after greeting his friend, sat down to dinner, but, on lifting the cover, said in surprise, "Dear me! I thought I had not dined, but I see I have."
So it went on for two full years, until Newton felt that his work was done. He divided it into three books. The first is entitled The Mathematical Principles of Natural Philosophy, and comprises about two hundred and fifty pages. It reminds one of a geometry, with its propositions, theorems, scholiums and problems. The first book is divided into fourteen sections and contains ninety-seven propositions, fifty theorems and forty-seven problems. Book II. discusses The Motions of Bodies. Here are found fifty-three propositions, forty-one