Hello all,
This one does not have the 24-cent stamp that I favor. But, it is a properly paid double weight letter for the 15 cent per quarter ounce rate (7.5 grams) established by the 1857 convention between the US and France. The letter was carried by the Cunard Line. Since it was a British contract ship, 24 cents of the 30 cents in postage were passed to France. France then compensated the British for the trans-Atlantic sailing and the transit through the UK and across the Channel.
Best to all!
Rob