JS Mill in his Principles (1848):
But though air is not wealth, mankind are much richer by obtaining it gratis, since the time and labour which would otherwise be required for supplying the most pressing of all wants, can be devoted to other purposes.
I am bewildered by the above sentence. Mill seems to be making a distinction between "riches" (or "being rich") and "wealth" (or "being wealthy"). But what is this distinction?