The air-whistle, or bell cord-code of signals, is standard upon all American railroads, and is as follows:

When the train is standing:

Two signals—start.
Three signals—back.
Four signals—apply or release air-brakes.
Five signals—call in flagman.

When the train is in motion:

Two signals—stop at once.
Three signals—stop at the next station.
Four signals—reduce speed.
Five signals—increase speed.

There also arises a necessity for communication between men who stand outside the train and who seek to guide the movement of the locomotive. This necessity has given rise to still another code, transmitted by the hands—holding a flag, if possible—by day, and a lighted lantern at night. This signal code follows:

Method of Transmitting Signal. Indication.
Swung across track. Stop.
Raised and lowered vertically. Proceed.
Swung vertically in a circle across the track:
When the train is standing— Back.
When train is in motion— Train has parted.
Swung horizontally in a circle:
When the train is standing— Apply air-brakes.
Held at arm’s length above head:
When the train is standing— Release air-brakes.
Any object waved violently by any person on
or near the track is a stop signal.

By use of his locomotive whistle, the engineer is enabled to acknowledge these signals, as well as to signal upon his own initiative. His code is also a standard in railroading. It follows:

—— A short blast.
———— A long blast.
—— Stop, apply brakes.
———— ———— Release brakes.
—— —— ———— ———— ————
—— ———— ———— ————		 Flagman go back and protect rear end of train.
———— ———— ———— ———— Flagman return to train.
———— ———— ———— Train in motion, has parted.
—— —— Acknowledgment of signals, not otherwise provided for.
—— —— —— Standing train—back.
—— —— —— —— Call for signals.
———— —— —— Calls attention to following section.
———— ———— —— —— Highway crossing signal.
———————— Approaching stations, junctions or railroad crossings at grade.

A succession of short blasts is an alarm for persons on the track and calls the attention of trainmen to danger ahead.