Why Does Red Mean Stop?
The 19th-century Scottish engineer Robert Stevenson, who was active in designing early lighthouses, (28) __________ for an alternative colour to white – most lighthouses had a white beacon – when he built a lighthouse near to one that already existed, because he was afraid ships wouldn’t be able to tell which was which.
Of the light sources and (29) __________ glasses available at the time, he found that red was a particularly intense light, meaning it could (30) __________ from the greatest distance.
So, in maritime signalling red became an alternative to white, and was later adopted by the Admiralty in 1852 (31) __________ the port-side on steam vessels. Green was adopted for the starboard-side, and vessels seeing the green light on (32) __________ ships had the right of way.
When train tracks were developed, engineers adopted this system as meaning stop and go – and the same system continued to be used with cars.
| A | to mark |
|---|---|
| B | marked |
| C | mark |
| D | was marked |