the context
before newton, many thought prisms created color. white light went in, glass did something, colors came out.
newton didn’t buy it, so he escalated.
experiment 1: single prism
white sunlight → prism → spectrum.
expected result. shows dispersion exists, but doesn’t yet kill the “glass modifies light” theory.
experiment 2: isolation test
single prism again, but now newton isolates one color (via aperture) and refracts it again.
result:
- red stays red
- blue stays blue
this strongly suggests colors are intrinsic, but skeptics could still wiggle.
experiment 3: the experimentum crucis
this is the crucial one.
- prism 1: white light → spectrum
- lens: recombine the spectrum back into white light
- prism 2: refract the recombined light again
result:
- the spectrum reappears exactly as before
boom.
if prisms created color, recombination should have “reset” things. instead, recombined white light behaves identically to original sunlight.
what this proves
- white light is a mixture of colors
- prisms only separate and recombine
- color is not added, distorted, or manufactured by glass