How it spread
Observations. At the end of the 19th century, an observer sketches a network of fine lines on the planet's disk, at the limit of what a telescope can resolve.
The name. He calls them by a word that in his language means both a natural waterway and a man-made canal.
The translation. English publications choose the second meaning. A description of the terrain becomes a report about structures.
The development. Another astronomer builds an observatory, draws maps of the network and publishes books about a civilization saving the planet from drying out.
The fourth step brought the idea to a wide audience. Books about a Martian civilization irrigating deserts with meltwater from the poles were taken as science and shaped Mars's image in popular culture for decades.
The observation itself was honest, though. At the limit of resolution, the eye tends to connect scattered spots into lines - and different observers, knowing about the lines, began to see them too.
How it ended
Images from passing spacecraft in the 1960s settled the question. They showed no lines - only craters, plains and dust. One series of photographs overturned half a century of observations.
Interestingly, some astronomers were already skeptical. Large telescopes did not show the lines, and some suggested that they were a feature of perception, not of the surface.
This story became a textbook example for two reasons. It shows both how translation can change meaning and how expectations affect what a person sees under difficult observing conditions.
Something useful came from it, too. The interest in Mars sparked by these books influenced several generations of researchers and largely determined why this particular planet is studied so closely.
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Sources
- Observations of linear structures on the surface of Mars in the late 19th century were described with a term that could mean either a natural waterway or an artificial canal
- in English, the second meaning became established. The existence of these structures was not confirmed when images from interplanetary spacecraft were captured in the 1960s