Leonardo seems to have occupied himself much with mechanical toys. He made mechanical birds that flew, mechanical lions that walked and a lizard which crawled and whose horns and eyes moved while the oscillating wings were constantly in motion. Every one of these contrivances, however, was the result of serious study. He took up with great assiduity the problem of flying and was quite sure that he would be able to make a machine by which men would accomplish locomotion through the air. He studied the wings of birds very carefully, and anticipated the knowledge of most of the principles of flight as they developed in later years. He used his mechanical lion as a bait to catch the attention of Francis I. The beast is said to have walked across the audience chamber towards the monarch until, when close to him, it stood up and disclosed the fact that the "Lily of France" was stamped upon its heart. Leonardo's own name is derived from lion and this was supposed to be his declaration of patriotic affection and loyalty to the French King. Something of the _busyness_ of his mind can be understood from the gossip that one hears about him in the letters of the time or even from what may be concluded from his own diary. It is said, for instance, that in the midst of the painting of the "Last Supper" there was quite an interruption in the work {29} because Leonardo became very much interested in the invention of a new machine for mincing meat and making sausages. The head of one of the Apostles was left unfinished for a time because Leonardo could not get the blades of the new machine fixed so as to make them more to his satisfaction. Unfriendly critics said that he would do anything so as to get away from his painting. Those who least understood declared that this was because he was trivial of mind and incapable of concentrating his attention. Anyone who has done artistic work of any kind, or indeed has devoted himself to literary work of any description, is likely to understand Leonardo's ways in such matters. The time comes when the particular vein of thought is exhausted for the moment and new ideas come slowly and with difficulty. The serious self-critical writer or artist recognizes that what he does at such times has not the significance he would like it to have and that he is likely to have to erase or greatly modify most of it afterwards or to regret it if he does not. If he is wise, then, he turns aside and gives his mind a complete rest by devoting it to something quite different from that in which he has been engaged before. If he insists on continuing his work after inspiration ceases or his particular vein of thought runs out, it becomes more and more difficult and more and more of a drudgery. Finally, unless he is almost entirely without proper self-appreciation, he literally has to give up the work that has become so difficult.