In the movie Young Tom Edison, the future inventor (played by Mickey Rooney) awaits his sister's return from a distant visit. To arrive home her train will cross a bridge that spans a wide river. Only word has reached Tom's town by telegraph that the bridge has been washed out.  Only trains don't have telegraph keys. Tom hops on a locomotive and races to stop his sister's train in time.  Rushing headlong toward the gorge he tugs feverishly on the loud steam whistle signalling in Morse Code THE BRIDGE IS OUT.  His sister deciphers the message and gets word to the engineer.. The train stops yards before total disaster. It got me to thinking . . .