“Why,” replied Joe, in answer to the volley of questions fired at him, “it wasn’t a hard thing at all. You know the big arms factories have a contrivance that tells them just how fast a bullet goes after it leaves the gun. They have two hoops set in a line say two hundred feet apart. These hoops are covered with a mesh of fine wires that are connected by electricity with a signal room. The bullet as it goes through the first hoop cuts a wire which registers the exact fraction of a second at which it is hit. The bullet strikes another wire as it goes through the second hoop and this also registers. Then all they have to do is to subtract the first time from the second and they have the exact time it has taken for the bullet to go that two hundred feet.”