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 NOTES.

I. 12.

our atmosphere the sun would appear a rayless orb of fire in the midst of a black concave. The equal diffusion of its light on earth is owing to the refraction of the rays by the atmosphere, and their reflection from other bodies. Light consists either of vibrations propagated through a subtle medium, or of numerous minute particles repelled in all directions from the luminous body. Its velocity greatly exceeds that of any substance with which we are acquainted: observations on the eclipses of Jupiter's satellites have demonstrated that light takes up no more than 8' 7" in passing from the sun to the earth, a distance of 95,000,000 miles. Some idea may be gained of the immense distance of the fixed stars, when it is computed that many years would elapse before light could reach this earth from the nearest of them; yet in one year light travels 5,422,400,000,000 miles, which is a distance 5,707,600 times greater than that of the sun from the earth.