‘Giving computers a sense of smell’: the quest to scientifically map odours

“Did you ever try to measure a smell?” Alexander Graham Bell once asked an audience of graduands at a high school in Washington DC.

He then quizzed the probably confused class of 1914 as to whether they could tell when one scent was twice the strength of another, or measure the difference between two distinct odours. Eventually, though, he came to the point: “Until you can measure their likenesses and difference, you can have no science of odour,” Bell said. “If you are ambitious to find a new science, measure a smell.”

At the time, scientists had an understanding that the sound and sight of Bell speaking on the stage could be described in terms of vibrations in the air and different wavelengths of light, but there was no comparable way of explaining the odours in the air that day in May. The mechanics of smell were a mystery, and in many ways they still are. “Unlike sound or vision – where the wavelength and amplitude clearly map to perceptual properties like tone frequency, colour or intensity