HOW TREATISE CAME TO BE WRITTEN 29 

 table that I subsequently evolved from them, my work was 

 sure to become twice as difficult to comprehend. For this 

 reason I have had them printed in duplicate, so that the 

 reader can tear one copy out and paste it on a card so as to 

 refer to it with greater ease if he cares to do so, without 

 injuring the book, for if he keeps them before his mind when 

 reading the rest of the treatise he will find it much easier to 

 understand this little work. 



