455. What is the constitution of the sun?
It is a spherical body, 1,384,472 times larger than the earth.
456. From what does the luminosity of the sun arise?
From a luminous atmosphere, or, as M. Arago named it, photosphere, which completely surrounds the body of the sun, and which is probably burning with great intensity.
457. What are the minor sources of light?
Light may be produced by chemical action, by electricity, and by phosphoresence, in the latter of which various agencies unite.
A ray of light is the smallest portion of light which we can recognise.
A medium is a body which affords a passage for the rays of light.