| Answer | Crossword Clue |
|---|---|
| heliography | the practice of signalling by heliograph |
| heliographies | HELIOGRAPHY, the practice of signalling by heliograph |
| heliograph | an apparatus for signalling by means of a movable mirror which reflects flashes of sunshine / to signal by heliograph |
| beckoning | the act of signalling by sign or gesture |
| beckonings | BECKONING, the act of signalling by sign or gesture |
| radiotelemetry | signalling by radiotelemeter, an instrument for measuring an electrical or other quantity and signalling the measurement to a distant point |
