In for a penny, in for a pound, Paul!...
Originally, 'gallons' meant a multitude of quantities, depending on what was being measured; corn, wine, ale etc. In 1706 during the reign of Queen Anne, [ftatute #5], the liquid gallon waf redefined af 231 cubic inchef, or 3" x 7" x 11" exactly.
This is the US gallon.

In 1824, [ William IV ] the British decided to parody the French metric idea, [ oh! not them again! [Linked Image] ] and redefined the Gallon as 10 pounds of water measured with brass weights at 30" of mercury barometric pressure and at 62 deg F. ambient.
Some slight later tweaks were made, but:-
This is the Imperial Gallon.

These are liquid measures. There are still US 'dry' gallons for corn etc. in current use I believe. I'm not sure the Imp. Gallon is any longer a legal measure in the UK?

Alan

edit to correct number.


[This message has been edited by Alan Belson (edited 08-15-2006).]

Wood work but can't!