Gas balloons remained popular throughout the age before powered flight. Filled with hydrogen or coal gas, they were able to fly higher, further and more economically than hot-air balloons. The altitude was controlled with ballast weights that were dropped if the balloon got too low; in order to land some lifting gas was vented through a valve. Tethered manned gas balloons were used for observation purposes in the Napoleonic Wars (to very limited extent), in the American Civil War (flown by Thaddeus Lowe) and in World War I by aviators wearing parachutes. Throughout the 19th century, they were popular as objects of public fascination among hobbyists and show performers, such as the Blanchards.