The dismal science

The phrase the dismal science refers to the discipline of economics.

The term drew a contrast with the phrase gay science which refers to song and verse writing

The phrase the dismal science first occurs in Thomas Carlyle's 1849 tract called Occasional Discourse on the Negro Question, in which he argued in favor of reintroducing slavery in order to regulate the labor market in the West Indies:
Not a "gay science," I should say, like some we have heard of; no, a dreary, desolate and, indeed, quite abject and distressing one; what we might call, by way of eminence, the dismal science.

Carlyle, Thomas (1849). "Occasional Discourse on the Negro Question", Fraser's Magazine for Town and Country, Vol. XL., p. 672.

Example: He is interested in history and the dismal science.