The simplicity with which nature had solved this mechanical problem filled him with enthusiasm: 'How subtle is this! How beautiful!'
He made a calculation, and the result added to his conviction that the mathematical sciences, with their laws founded on the essential necessities of reason, justified the natural necessities of mechanics.
Hour after hour flew by unnoticed, and evening came on. After supper, and relaxation in talk with his pupils, he again set to work. The acumen and lucidity of his thoughts convinced him that he was on the verge of some great discovery.
'Behold how the wind, blowing across the fields, drives waves over the rye, one succeeding the other, while the stalks, though they bend, remain fixed in the ground! In like manner do the waves run over the immovable water. The ripple caused by the throwing of a stone, or by the force of the wind, should rather be called a shiver than a movement of the water. And of this you may persuade yourself by throwing a straw into the widening rings of wavelets, and watching how it rises and falls, but does not leave its place.'
This experiment with the straw reminded him of a similar test which he had applied when studying the waves of sound. He mused—
'The striking of a bell will induce a slight quiver and a low resonance in a neighbouring bell; a note sounded on a lute will awake the same note in a lute by its side; and a straw laid upon the string which produces that note will show its vibration.'
The soul of the student was greatly stirred; he divined some connection, a whole world of undiscovered knowledge, between the two oscillating straws; the one trembling on the surface of the waves, the other quivering on the vibrating string. And an idea, swift as lightning, flashed across his mind.
'The mechanical law is the same in the two cases! Like the waves on the water when a stone drops into it, so the waves of sound widen in the air, intersecting others, but not mingling with them, keeping their own centre in the place of their origin. What, then, of light? As an echo is the reproduction of a sound, the reflection in a mirror is an echo of light. There is but one mechanical law in all the phenomena of physical force; there is but one will; and this will is thy justice, O Prime Mover! the angle of incidence must be equal to the angle of reflection.'
His face pale, his eyes burning with enthusiasm, Leonardo felt that once again, and this time more certainly than before, he was about to sound an abyss into which no man had looked before. He knew that this discovery, if confirmed by experiment, was the greatest mechanical discovery since the days of Archimedes. Two months ago, when he had heard that Vasco di Gama had doubled the Cape of Good Hope and discovered a new route to India, Leonardo had envied him, but now he had made a greater discovery than di Gama or Columbus; he had sighted more mysterious expanses, and no less than they had found a new heaven and a new earth.
But through the wall there reached his ears the groans and the ravings of the sufferer. He listened, and remembered his mechanics, the senseless destruction of the Colossus, the inevitable ruin of the Cenacolo, Astro's foolish and horrible fall; and asked himself:—