On June 1, 1862, Thaddeus Lowe floated a thousand feet above a fierce Civil War battle raging just outside the Confederate capital of Richmond, Virginia. From the wicker basket dangling under his silk hydrogen balloon, the aeronaut telegraphed a message to Northern generals on the ground: Union troops were finally driving back the Confederate forces. Lowe’s message was transmitted to the War Department in Washington a hundred miles away, where President Abraham Lincoln read his flying spy’s good news with relief.