E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A custom formerly observed every three years by the boys of Eton school, who proceeded on Whit Tuesday ad montem (to a mound called Salt Hill), near the Bath Road, and exacted a gratuity called salt from all who passed by. Sometimes as much as £1,000 was thus collected. The custom was abolished in 1847.