How does John Stuart Mill distinguish between "wealth" and "riches"? 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 &quot;riches&quot; (or &quot;being rich&quot;) and &quot;wealth&quot; (or &quot;being wealthy&quot;). But what is this distinction?
I can only speculate on what Mill meant, but it seems to me that

This is mostly a figure of speech. People sometimes say things like &quot;I have no money, but I am wealthy in other ways&quot;, meaning they have something they would not trade for money, i.e. monetary wealth.
If there is a distinction, it is in the concept of ownership. Air is not wealth because I do not own it. There are several things that are beneficial to have (that enrich us) that we do not own and could not easily trade. Health, loved ones, air, etc. One can have, but not own these things, so they are not wealth.
(Except in Spaceballs.)