Conversation so far:
What was Modern Painters I?
What became the first volume of Modern Painters (1843), published by Smith, Elder & Co.
under the anonymous but authoritative title, "A Graduate of Oxford.
What was the outcome of Modern Painters?
CANNOTANSWER.
Was there a second volume?
CANNOTANSWER.

Question: What was it about?
Self-contained rewrite: What was Modern Painters I by John Ruskin about?