the stars; for the reason, that the rays, coming from all parts of their disk, at once are intermingled, and of necessity produce white. This difficulty did not exist in similar investigations on the sun, because its disk is so large, that the rays from any one part of it may be examined while the others are excluded. Under these circumstances, further proof might seem to be hopeless; but advantage was taken of the fact, that there are certain stars which are sometimes light, sometimes dark, either from having a movement of rotation on their own axis, or because they are occasionally eclipsed by a non-luminous satellite revolving around them. It is clear, that while the light is waxing or waning, it comes from a part only of the star's disk; consequently, the neutralisation of rays, which takes place when they depart from the whole surface at once, cannot then occur; and from the observations on the portion of light thus transmitted, and which is found to remain white under all its phases, we are entitled to conclude, in M. Arago's words, that 'our sun is a star, and that its physical constitution is identical with that of the millions of stars strewn in the firmament.'
