The best Quotations

Do you know the writers of the following quotations?

Quotation I who have been involved with all styles of painting can assure you that the only things that fluctuate are the waves of fashion which carry the snobs and speculators; the number of true connoisseurs remains more or less the same. - writer
Quotation I could never think well of a man's intellectual or moral character, if he was habitually unfaithful to his appointments. - writer
Quotation Sanity is a madness put to good uses; waking life is a dream controlled. - writer
Quotation Speech is of time, silence is of eternity. - writer
Quotation Conform and be dull. - writer
Quotation The only thing that we know is that we know nothing and that is the highest flight of human wisdom. - writer