6. Blue.
7. Indigo—a dark and intense blue.
8. Violet—blue mingled with red.
9. Lavender grey—a neutral tint.
10. Rays called fluorescent, which are either of a pure silvery blue, or a delicate green.
465. Why is a ray of light, which contains these elementary rays, white?
Because the colour of light is governed by the rapidity of the vibrations of the ether-waves. When a ray of light is refracted by, or transmitted through a body, its vibrations are frequently disturbed and altered, and thus a different impression is made upon the eye.
Light which gives 37,640 vibrations in an inch, or 458,000,000,000,000 in a second of time, produces that sensation upon the eye which makes the object that directs the vibrations appear red. Yellow light requires 44,000 vibrations in an inch, and 535,000,000,000,000 in a second of time. And the other colours enumerated (see [464]) all require different velocities of vibration to produce the colours by which they are distinguished.
"The light of the body is the eye: if therefore thine eye be single, thy whole body shall be full of light."—Matt. v.