Philip Dormer Stanhope, Earl of Chesterfield 
Letters to His Son on the Art of Becoming a Man of the World and a Gentleman, 1748 [EPUB ebook] 

pub One.info present you this new edition. DEAR BOY: I am edified with the allotment of your time at Leipsig; which is so well employed from morning till night, that a fool would say you had none left for yourself; whereas, I am sure you have sense enough to know, that such a right use of your time is having it all to yourself; nay, it is even more, for it is laying it out to immense interest, which, in a very few years, will amount to a prodigious capital.