Newton's Optics

How Newton broke light apart and started a war with Robert Hooke.

The prism experiments

In 1665–1666, during his annus mirabilis at Woolsthorpe (sent home from Cambridge by the plague), Newton bought a glass prism at Stourbridge Fair and began experimenting. He darkened his room, let a thin beam of sunlight through a hole in the shutter, and passed it through the prism. White light fanned out into the spectrum: red, orange, yellow, green, blue, indigo, violet.

This was not new — prisms had been toys for decades. What Newton did next was new: he passed a single color from the first prism through a second prism. It didn’t split further. This proved that the colors were not created by the prism (the prevailing theory) but were already present in white light. The prism merely separated them.

The bodkin experiments

Newton didn’t stop at prisms. He stared directly at the sun until he nearly went blind, cataloguing the afterimages in a dark room for days. He stuck a bodkin (a blunt needle) between his eyeball and its socket to study how pressure distorted vision — pressing on the eye produced colored rings, which told him something about how the eye processed light. He recorded all of this in his notebooks with clinical precision and hand-drawn diagrams.

These experiments were dangerous but not irrational. Newton was trying to determine whether color was a property of light itself or a product of the eye’s mechanism. The answer (both, in different ways) connects his optics work to his later philosophical commitments about the nature of reality.

The 1672 paper and the Hooke feud

Newton published his findings in a 1672 paper for the Royal Society. Robert Hooke, as curator of experiments, criticized it — arguing that light behaved as a wave (Hooke’s view) rather than as particles or “corpuscles” (Newton’s view). Newton was so enraged by the criticism that he nearly withdrew from scientific life entirely. He wouldn’t publish his full Opticks until 1704 — the year after Hooke died. The timing was not coincidental.

Corpuscles vs. waves

Newton argued light was made of tiny particles (corpuscles) traveling in straight lines. Hooke and Christiaan Huygens argued it was a wave, like sound. Both sides had evidence. Newton’s particle theory explained sharp shadows and the straight-line behavior of light. Hooke’s wave theory explained diffraction and interference patterns.

The debate wouldn’t be resolved for two centuries. Thomas Young’s double-slit experiment (1801) seemed to prove waves. Then quantum mechanics revealed that light is both — wave and particle simultaneously. Newton and Hooke were each half right.

In the novel

Daniel witnesses Newton’s self-experimentation firsthand — the bodkin in the eye, the sun-staring, the prism work. These scenes establish Newton as simultaneously brilliant and terrifying: a man willing to damage his own body to extract data from nature. The optics work also connects to the novel’s theme of light as knowledge — the Scientific Revolution as a process of making the invisible visible.