The cast-metal bracket attached to the moving arm of a semaphore signal, designed to hold colored glass roundels. As the signal arm moves to change the aspect, the spectacle swings in front of a stationary oil or electric lamp, changing the color of the light displayed to approaching trains at night.
Heard on the job
The glass in the spectacle was shattered, so the signal showed a white light instead of red.
Also heard as
- spectacle plate