David Todd was an American astronomer, director of the Observatory at Amherst College, who was interested in the possibility of radio communication with Mars. In 1907, Todd led the Lowell expedition to Chile to photograph the Martian canals. Two years later, he suggested that the Martians might use radio waves to communicate with Earth and that sensitive receivers carried to high altitude by balloon would have the best chance of picking up these signals. Although Todd revived his plan in 1920, around the time Marconi was discussing extraterrestrial signals, no balloon was ever launched. In August 1924, during an opposition of Mars, Todd persuaded the United States Army and Navy to use their receiving stations to listen in for any unusual signals.