A raven, perishing with thirst saw, that a jug, and hoping to find water, flied to it with admiration. When it has reached it, it has found out to it I burn, that it contained so not enough water, that it could not reach probably it. It tried everything, that it could think to reach some water, but all its efforts were vainly. At last it has collected so many stones as it could bear and has lowered their one behind another with its beak in a jug while it has not brought water within the limits of its reach and thus has rescued its life. Need - mother of the invention.