whatever melancholic speculators may assert, it seems a well-ascertained fact, that in all times, reckoning even from those of the Heraclides and Pelasgi, the happiness and greatness of mankind at large have been continually progressive
Interesting shift in tone in this section. He seems to be saying that despite the fact that society has recently become preoccupied machines, sciences etc, it will nevertheless continue to grow and improve - faith in human nature?
several mythological references throughout - contrast between the old world and the new.