It was late in the summer of 1894 when Charles Thomson Rees Wilson was first beguiled by phantoms. The 25-year-old Scot – son of a farmer from a long line of farmers – had developed an interest in meteorology and other physical sciences while studying at what is now the University of Manchester, and he had travelled to the summit of Ben Nevis, a mountain in Scotland and site of the highest point in the U.K. , to work for a couple of weeks at the meteorological observatory there. It was during this visit that Wilson first encountered the Brocken spectre.
The Brocken spectre appeared as a dark, silent figure in the distance, surrounded by an eerie halo of color and light. Such visions – first described in association with a German mountain known as the Brocken – had been the subject of folklore for centuries, but Wilson, being a good Scottish scientist, recognized the image for what it was: his own shadow, cast by the sun behind him, falling on fog further down the mountainside, and surrounded by a circle of reflected sunlight known as a glory. Still, knowing the rational explanation did not make Wilson any less fascinated by the ethereal phenomenon. He left Ben Nevis wondering how he could duplicate the effect himself.
To do this, Wilson decided, he would need to find a way to create at will the clouds that captured the shadow and reflected the light. Within a few months in the laboratory, he had created a cloud-making device. The air inside a glass globe would be supersaturated with water vapor, and then the air pressure lowered mechanically. This would cause the condensation of the vapor, causing a cloud to form in the globe. A neat trick, to be sure; clearly enough to impress a farmer boy, but not really a huge scientific leap, now, was it?
But the same curiosity, intelligence, and keen sense of observation that had led Wilson to build his new machine would lead him to discover its astounding and unprecedented scientific uses. He noticed that drops of condensation would sometimes form within the glass globe – similar to the condensation that would naturally be generated by the presence of dust particles – no matter how carefully he kept the machine and its contents clean. Rather than dismiss the drops as resulting from unseen but unavoidable grit, he considered alternative explanations, and eventually concluded that the only thing that made sense was that ions – individual atoms that had gained a positive or negative electric charge – were the seed for these drops. An ion could be caused just by the static electricity generated by operating the machine, and of course would be invisible to the naked eye.
To test this theory, Wilson decided to intentionally create ions within his machine, which he now called a “cloud chamber”. It had recently been discovered that the radiation emitted by elements like radium could change the electric charge of atoms, turning them into ions, and so Wilson exposed his cloud chamber to such radiation. What he saw then was not mere drops of condensation, but rays and whorls – paths of condensation caused as the radiation passed through the cloud chamber, sometimes in straight lines, and sometimes curving or ricocheting as the radiation was somehow affected by its environment.
Wilson realized he had discovered a way to see the unseen – to make observations of the behavior of particles far too small to be observed directly. The paths of condensation in the cloud chamber would fade quickly, but not so quickly that they could not be captured in photographs. Measurements of the angles and curves of the paths would eventually teach scientists amazing things about the mechanisms of radiation – alpha-particles, beta-particles, electrons – and the structure of the atom. Ernest Rutherford, the “father of nuclear physics”, would describe the cloud chamber as “the most original and wonderful instrument in scientific history”.
In 1927, C.T.R. Wilson was awarded the Nobel Prize in Physics for his invention of the cloud chamber. Could he have foreseen or even imagined such an honor as he came down from Ben Nevis back in 1894, entranced by the Brocken spectre? Of course not. For one thing, Alfred Nobel wasn’t dead yet. But we don’t always take a straight path to our successes. Sometimes the most important thing is to just ramble someplace new and exciting, always remaining attentive to the novelties we find there.