Stamp giveaway series 2, # 26 [solved]

Universal Postal Union (Bolivia (2 souvenir sheets); Guinea-Bissau (set plus souvenir sheet); Paraguay (souvenir sheet, also UN stamps anniversary)

What material was used in balls that were supposed contain messages and float down a river to a besieged city in 19th century Europe? The effort was not successful. What probably prevented the receipt of the balls until after the surrender of the city?

The competition is open to everyone. Enter as often as you wish. The winning entry will be the first received with the correct answers to both questions at or before 8 PM July 28, 2022 eastern US time. If no correct response with answers to both questions is received, the first with one correct answer will win. If no correct answers are received, the first response wins. My decision of the winner is final.

Good luck to all who choose to participate!

Will

Hollow balls made of zinc!  The siege of Paris.  Probably the Seine froze, preventing the messages from arriving.

I don't know why zinc was a good material for this, or if it ever had a good chance of being successful.

The method that was actually successful was a combination of balloons and homing pigeons!

I also think zinc balls during the site of Paris in 1871. The balls were intended to sink to the bottom of the Seine and then rolled to their destination by the strong current.

Many balls were probably snatched behind obstacles on the bottom of the river, thus preventing them to roll while others just went through the nets that were meant to catch the balls because chunks of ice floating downriver had destroyed most nets.

Another attempt that didn't work was sending 5 sheepdogs from Paris in a balloon and freeing them upon landing. They were never seen again. 

An interesting article I ran across researching this: https://www.atlasobscura.com/articles/pigeon-balloon-memorial-paris-bartholdi 

There is a commemorative medal shown that I couldn't find in the Numista catalogue, though I am not convinced that I exhausted the search possibilities.

I see you have commented but not declared a winner… Regarding the question “What probably prevented the receipt of the balls until after the surrender of the city?” I will make my guess more specific to say that winter arrived and the Seine was too cold and icy to safely enter to retrieve the zinc balls.

Zinc balls used in Paris, during the Franco-Prussian War. I think the reason they failed to arrive was because the Prussian artillery used the balls for target practice. 

Zinc balls during the siege of Paris in 1871.  They were stopped by dams.

I declare rsirian1 and Newtony co-winners! The answer I was looking for for question 2 was “The Prussians kept the locks from operating until after the surrender of the city. Some balls with messages were recovered once the locks starting operating.”

While locks are not dams, they are close enough to be considered a possible answer. The same with the theory of the balls being prevented from rolling by obstacles on the bottom of the river.

The prize that has been noted will go to Newtony and I will put together another prize for rsirian1.

Thanks to all the creative entries (and the creative Frenchmen of the 19th century!). Watch for future entries!

Will 

Thank you very much!

I didn't think about any locks! Seems obvious now you mention it 👍

In addition, some of these Moulins balls were found several years later; two Last ones with their mails in 1968 and in 1982 ! I guess the   rightholders were surprised to receive à message written in 1870/1…

I was convinced that winter had something to do with the reason!  Anyway, always glad to learn something new.  Is it documented if the Prussians shut down the locks to interrupt this communication, or was that just a side effect of restricting traffic on the river in general?

I think the locks were shut down just to limit river traffic  of any kind and that the Prussians that early in the siege were not familiar with any French plans for communication. Early in the siege (when locks already were shut down) the Prussians discovered a “secret” telegraph system set up by the French and had not yet attempted to use the metal balls. Winter and the freezing of the river did shut down plans to float messages in glass balls that were to look like river bubbles!

Will

Thanks, Will!

The stamps also reached Belgium.

Thank you very much!