'The visits of angels are short and far between' is an old proverb. The expression, however, was altered by Thomas Campbell (THE PLEASURES OF HOPE) to
What though my winged hours of bliss have been,
Like angel visits, few and far between?
The original thought has been ruined because the alliterative alteration, "few and far between," though more pleasing to the ear, actually means the same thing in relation to visits [according to Hazlitt, in his LECTURES ON THE ENGLISH POETS]. This is another example of "improvements" being made to a sensible, but forgotten, original saying.
Information on the above was derived from A DICTIONARY OF CONTEMPORARY AMERICAN USAGE, by Bergan Evans and Cornelia Evans, page 176.