As every divided kingdom falls, so every mind divided between many studies confounds and saps itself. - Leonardo da Vinci

I am fully conscious that, not being a literary man , certain presumptuous persons will think that they may reasonably blame me; alleging that I am not a man of letters. Foolish folks! do they not know that I might retort as Marius did to the Roman Patricians by saying: That they, who deck themselves out in the labours of others will not allow me my own. They will say that I, having no literary skill, cannot properly express that which I desire to treat of, but they do not know that my subjects are to be dealt with by experience rather than by words; and experience has been the mistress of those who wrote well. And so, as mistress, I will cite her in all cases.

It vexes me greatly that having to earn my living has forced me to interrupt the work and to attend to small matters.

Happy will be those who give ear to the words of the dead:—The reading of good works and the observing of their precepts.