E. Cobham Brewer 1810–1897. Dictionary of Phrase and Fable. 1898.
Pilot Balloon (A).
A political feeler; a hint thrown out to ascertain public opinion on some moot point.
1
“As this gentleman is in the confidence of ministers, it is fair to assume that he was deputed to start this statement as a pilot balloon.”—Newspaper leader, 1885.
