Full Idea
Art is a human activity in which one man consciously by means of external signs, hands on to others feelings he has lived through, and other are infected by those feelings, and also experience them.
Gist of Idea
Art is when one man uses external signs to hand on his feelings to another man
Source
Leo Tolstoy (What is Art? [1898], Ch.5)
Book Reference
Tolstoy,Leo: 'What is Art? and Essays on Art', ed/tr. Maude,A [OUP 1975], p.123
A Reaction
Such definitions always work better for some art forms than for others. This may fit 'Anna Karenin' quite well, but probably not Bach's 'Art of Fugue'. Writing obscenities on someone's front door would fit this definition.