Railway semaphore
device · 1841 · Industrial Revolution
A signal that allows or forbids movement.
What it is made of
- Signal post — has part. A post.
- Semaphore arm — has part. The position of the arm is the signal.
- Signal wire — has part. A cable from the control post.
- Railway signal lamp — has part. A night signal.
Principles and materials it uses
- Lever — uses. The semaphore is set by a lever.
- Wood — is made of. The semaphore arm is wooden.
- Cast iron — is made of. On a cast-iron mast.
Where it is used
- Automatic block signalling — is part of. Signals.
History: what it evolved from and what it influenced
- Optical telegraph — evolved from. The semaphore idea.
- Traffic light — evolved into. The first traffic light was a railway-style semaphore.