This is from a letter of 8 February 1780 from BENJAMIN FRANKLIN to Joseph Priestly (known to chemists as the "discoverer" of oxygen)
The rapid progress true science now makes, occasions my regretting sometimes that I was born too soon. It is impossible to imagine the height to which may be carried, in a thousand years, the power of man over matter. We may perhaps learn to deprive large masses of their gravity, and give them absolute levity, for the sake of easy transport. Agriculture may diminish its labour and double its produce, all diseases may by sure means be prevented or cured, not excepting even that of old age, and our lives lengthened at pleasure even beyond the antediluvian standard. O that moral science were in so fair a way of improvement, that men would cease to be wolves of one another, and that human beings would at length learn what they now improperly call humanity!
It was quoted in the introduction of a book called How Mumbo-Jumbo Conquered the World by Francis Wheen. It looks very interesting indeed. Publishers Weekly described it as a "full-frontal assault on the past 25 years of 'Counter-Enlightenment idiocy.'" (Good description of how the world has turned frighteningly superstitious.)