74 THE LIFE OF SCIENCE 



such as we find, for instance, in the writings of Roger Bacon; but, 

 on the contrary, very definite and clear ideas which could have 

 been patented, if such a thing as a patent office had already 

 existed! Moreover, a number of these drawings are so elaborate, 

 giving us general views of the whole machine from different direc- 

 tions, and minute sketches of every single piece and of every 

 detail of importance — that it would be easy enough to reconstruct 

 it. In many cases, however, that is not even necessary, since these 

 machines were actually constructed and used, some of them 

 almost to our own time. 



To visualize better the activity of his mind, let us take at ran- 

 dom a few years of his life and watch him at work. We might 

 take, for instance, those years of divine inspiration when he was 

 painting the "Last Supper" in the refectory of Santa Maria delle 

 Grazie, that is, about 1494-98. Do you suppose that this vast 

 undertaking claimed the whole of his attention? 



During these few years we see him act professionally as a 

 pageant master, a decorator, an architect, an hydraulic engineer. 

 His friend, Fra Luca Pacioli, the mathematician, tells us that by 

 1498 Leonardo "had completed with the greatest care his book on 

 painting and on the movements of the human figure." We also 

 know that before 1499, he had painted the portraits of Cecilia 

 Gallerani and of Lucrezia Crivelli. Besides, his note-books of that 

 period show that he was interested in a great variety of other 

 subjects, chief among them hydraulics, flying, optics, dynamics, 

 zoology, and the construction of various machines. He was also 

 making a study of his own language, and preparing a sort of 

 Italian dictionary. No wonder that the prior of Santa Maria com- 

 plained of his slowness! 



It so happened that during these four years he did not do much 

 anatomical work, but during almost any other period he would 

 have been carrying on some dissecting. Corpses were always hard 

 to get, and I suppose that when he could get hold of one he made 

 the most of it, working day and night as fast as he could. Then, 



