The concept of Significant Form was devised by Clive Bell (1881-1964) in his book Art (1914). Bell was an English art critic, a member of the Bloomsbury Group, and the husband of Vanessa Stephen (Virginia Woolf's sister).
Bell argued (rather like Roger Fry, whose ideas were discussed earlier) that the only relevant aspects of a work of art are its physical properties, and that its historical context and what it represents are both irrelevant to its appreciation.
The quote which Sebastian reads from Bell's Art ("Does anyone feel the same kind of emotion for a butterfly or a flower that he feels for a cathedral or a picture?") comes from the first chapter entitled 'The Aesthetic Hypothesis'.
Click here to read Art on-line.