Electromagnetic Wave
Light, Sound and Waves

Blondlot’s N-rays

Stories from Physics for 11-14 14-16 IOP RESOURCES

French physicist Prosper-René Blondlot demonstrated that X-rays travelled at the speed of light. But he is perhaps now best remembered for his work on N-rays. Blondlot investigated the effect of X-rays on electrical sparks and, in 1903, concluded that an additional form of radiation was causing changes to the brightness of the spark. He labelled the radiation N-rays and carried out a series of experiments to deduce further properties of the rays, noting that they were emitted by the Sun and materials under strain and that they influenced organic matter.

Other scientists followed up his work and published research on N-rays, with one researcher reporting that his desk plant emitted the radiation. Though supportive studies appeared for a number of years after Blondlot’s ‘discovery’, the American physicist, Robert H Wood, visited Blondlot’s laboratory in 1904 and debunked the N-ray phenomenon by observing that Blondlot’s observations were caused by psycho-physiological effects.

Aptly, Wood’s career in physics had been spurred by a personal experience of ‘invisible rays’. As a boy, Wood had been intent on becoming a priest but after seeing an aurora chose to study physics instead to understand the ‘invisible rays’ that caused the phenomenon.

The incident is often cited as a demonstration of the dangers of experimenter bias.


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