The 19th-Century Trippers Who Probed the Mind

Nullius in Verba—Nothing on authority. In 1660, on the eve of its founding, The Royal Society of London took this defiant Latin phrase as its motto. For the United Kingdom’s main scientific body, it announced a new way of thinking that came to dominate the scientific revolution: Classical and scholastic authority could prove apocryphal. Only direct evidence, generated by experiment and first-person observation, revealed scientific truth.

Evidence was everything, and leading scientists of the era, including Isaac Newton and Robert Boyle, developed a system for classifying it. Qualities such as size, shape, or weight, which were directly measurable, were referred to as “primary” evidence. Texture, taste, or feelings that described human sensations and responses were considered “secondary.” While primary evidence was easier to collect and test, sensation and perception were considered legitimate fields of inquiry, and certain classes of data could only be demonstrated by self-experiment.

“I feel like the sound of a harp.”

In a famous and graphic example, when Isaac Newton wished to establish whether a change in the curvature of the eye would present a distorted image to the perceiver, he took a large needle, or bodkin, and stuck it as far into his eye as he could. He then described in detail the colored circles that appeared to him. It was not possible to present direct evidence for these shapes, since they only existed in Newton’s