Line of Beauty
according to Hogarth, is a curve thus. Mengs was of the same opinion, but thought it should be more serpentine. Of course, these fancies are not tenable, for the line which may be beautiful for one object would be hideous in another. What would Hogarth have said to a nose or mouth which followed his line of beauty?
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894