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The Rudolf Steiner Archive

a project of Steiner Online Library, a public charity

Cosmology and Human Evolution
Color Theory
GA 91

The Theory of Color and Light IV

6 August 1903, Berlin

Until the nineteenth century, the substance theory or emission hypothesis—emission of a light substance—was valid for the explanation of light phenomena, because it was not possible to refute this theory physically by experiments. The correctness of the substance theory depends on the fact that light added to light gives greater brightness.

In the nineteenth century Fresnel proved by experiment that light is a motion, a vibration. Light is vibrating motion. The proof lies in the fact that light brought to light can result in darkness.

The law of reflection is: a ray of light is reflected back from a reflecting wall in such a way that the angle of incidence is equal to the angle of reflection.

Reflected Light
Figure 1. Reflected Light

This law is found as follows: We place a light in front of a mirror and receive the reflected beam in our eye. Between the lines of the Sun's outgoing rays and its reflected ones we draw a perpendicular line and in this way we get two acute angles. We call the first angle (angle A) angle of incidence, the second one (angle B) angle of reflection (subjective experiment).

The 's reflection in a darkroom
Figure 2. The Sun's reflection in a darkroom

The same law applies to the objective experiment: we let a ray of light enter through an aperture onto a mirror in a darkroom; we get the Sun's light reflected onto the opposite screen: at the point of intersection, the perpendicularly drawn line gives the two equal acute angles: angle of incidence and angle of reflection.

If we now set up two mirrors with angles inclined to one another, from the two mirrors the received light image is reflected back in such a way that one Sun disk coincides with the other.—We can then have either light or dark. Light added to light can give darkness.

From this it follows with irrefutable force of proof that light is not matter (for then matter added to matter would give more light) but motion. In motion, vibrating particles can be accelerated by a new impulse in the same direction, that is, amplified, or inhibited and brought to a standstill when they collide. Light is vibrating motion.

If we let the light rays fall on the mirror through a grating, the reflection on the screen gives light and dark side by side.

Motion presupposes a substance which is set in vibration. This is the ether. The Sun's rays vibrate in four different types of ether. They yield heat, light and chemical effects; in their finest state they are the substance of life—prana (life ether). Thus, in our physical matter we have solid, liquid, gas, and four etheric types. We find them in the plant:

  1. The plant takes in matter and transforms it (chemical/formative ether).
  2. The plant shows its parts colored (light ether).
  3. The plant needs warmth for its activity (warmth ether).