From the weird and fascinating An Essay on Public Happiness, published in 1774.
If, on the contrary, there should exist a nation which, without being very numerous, possesses a great quantity of well-cultivated lands; which daily increases its agriculture, and its commerce, whilst its population doth not increase in a similar proportion; and which, in short, raises a much greater measure of subsistence, without maintaining a greater number of inhabitants, I affirm that this nation must consume specifically more than other nations; and that, here the tariff of human life is higher than elsewhere. This, then, is the surest sign of the felicity of mankind.
Chastellux was third in command of the French troops at Yorktown, corresponded with Jefferson, Adams, Washington, etc., was a protege of Voltaire, and member of the Academie Francaise. Chastellux, who was also the first volunteer to be vaccinated for smallpox (there was of course a tremendous controversy over whether we should be “playing God” by curing people of horrible diseases) may have been more of a scientific materialist than his somewhat more pious yet still very science-besotted American correspondants.
Here is my favorite passage from Chastellux's Essay:
Anatomy hath lifted up the veil of humanity; it hath discovered an innumerable quantity of machines, which give motion to these frivolous decorations of life, and proved to us that Moses made use of extremely bold hyperbole, when he asserted that God created man after his own image. This science, at once terrible and useful, hath taught those destructive weapons, which were accustomed to deprive us of our being, the new art of preserving it, and tracing out for them, even in our very entrails, a dark, but certin road, hath enabled the artist to remedy those disorders which he could not see.
That is, when we get over Moses' flattering lie and realize that we are meat-machines, we can transform the knife to the scalpel and actually improve human life. Chastellux plumped for a science of politics that would increase human happiness, by which he clearly meant: consumption per capita.
Bonus: If you'd like to know what the Enlightenment French scientific elite thought of Benjamin Franklin, here you go:
A great, and magnificent discovery was reserved for these times; and this is Electricity, the terrible effects of which have placed mankind on an equality with the gods of antiquity, whilst Franklin, like another Prometheus, acquired the art of stealing the celestial fire, and rendering it docile to his laws.
That's a good review.