“Angels’ share” is an endearing term which describes the loss of water and alcohol (depending on humidity) from the barrel during storage. The oak soaks up a lot of liquid when first put into service, then, while some oxygen seeps into the wine, some liquid also evaporates. The Angels’ Share can amount to 2-3 gallons of wine over time. As a result, the barrels need to be topped off occasionally.
Allan Pinkerton, best known for the detective agency he started in the mid-1800s, was originally a cooper. In 1861, he helped to save the life president-elect Abraham Lincoln by foiling an assassination attempt by Southern loyalists who planned to shoot him during a stopover in Baltimore on his way to Washington DC to be sworn in. Pinkerton devised a rather clever and sophisticated ‘detour’ to keep him safe. The Pinkerton Consulting and Investigations agency is still active today!
During his reign, Napoleon, became concerned about the availability of wood for shipbuilding. So he decided to solve the problem by planting five brand new oak forests. Oak has since been outshined by other woods for boat construction, so the oak is now used to make some of the finest wine barrels in the world.
Wikipedia, Smithsonian Magazine and my own research.