The phrase ‘Commerce of Light’ is taken from Bernard le Bovier de Fontenelle’s widely disseminated scientific dialogue, Entretiens sur la pluralité des mondes (1686). It’s a witty and charmingly flirtatious set of exchanges between a Philosopher and a beautiful young Marquiese, where the former enlightens the latter in the new Copernican astronomy.

The Philosopher employs an image of each heavenly body as ‘like a Balloon’ (160), constantly inflating and deflating. This image alone enchants the Marquiese and, in telling imagery of her own, inspires her with a vision of a perpetual competition between bodies that is, at the same time, co-operative and social—and perhaps, in its ‘swell and fall’, somewhat erotic:

I am extreamly in love, said the Marquiese, with these Idea’s you give me of the Balloons, which swell and fall every Moment; and those Worlds, which are always jostling together: But, above all, I am pleas’d to consider, that this Strife amongst ‘em produces a Commerce of Light, which is the only Traffick they can have. (160)

The pleasure she takes in this suggests both the pleasures and contradictions of Enlightenment sociability itself, and that ideological defence of individualistic commercial interchange (the ‘jostling together’ of the market-place) as benevolent, generating Enlightenment in the form of a ‘Commerce of Light’ that is typical of the age.