The history of drop towers goes back to at least 1769, when a “drop process” was patented by Englishman William Watts, who was looking for a better way to make shot for muskets. Watts’ process was based on the principle that a liquid will form a perfect sphere while in free fall because of surface tension.
Watts ingeniously applied this concept to molten lead, reasoning that it would form perfectly round balls when allowed to free fall a certain distance. To test this theory, he extended his three story house to six stories and constructed a shot tower. And he was right: his shot tower produced lead shot that was far superior to that made from molds. Watts’ insight revolutionized the production of musket balls.
The procedure was simple. Molten lead was poured onto a copper plate containing holes of different sizes (in effect a sieve) that produced droplets of different sizes. The lead fell freely through a shaft, forming into spheres during the descent before landing in a water-filled kettle, which served to stop and cool the lead. The shot was then dried, polished and put into bags for distribution.
The Sparks Shot Tower in Philadelphia was among the first shot towers in the U.S. The tower was built in 1808 by Thomas Sparks and John Bishop as a result of the Embargo Act imposed by President Jefferson, which prohibited the importation of, among other things, high-quality shot. Sparks’ and Bishop’s 142-foot-high brick tower tapered from a base with a 30-foot circumference to a top with a 15-foot circumference. Known as the Sparks Shot Tower, it still stands on the Delaware River waterfront at Carpenter Street in South Philadelphia.
Another well-known shot tower still in existence is the Shot Tower in Wythe County, Virginia. The tower was built by local miner Thomas Jackson, who completed it in 1807 after seven years of construction. It’s shaft measures 150 feet in height, but only the top half is above ground (as can be seen in a diagram of the tower).
Today, there are only a handful of shot towers in existence in the U.S. And each one is majestic in its own right, as befits an architecture that soars.