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Our first answer to this theory is that the number of moving stars (planets) is fixed. It is quite usual for them and comets to appear at the same time; whence it is manifest that the comet is not due to the conjunction of planets, but is a distinctive independent star. Besides, it is a matter of frequent occurrence for a star to come under the orbit of a more elevated star. Saturn, for example, is sometimes above Jupiter; Mars looks down in a straight line on Venus or Mercury. But yet no comet is formed from this movement whereby the one planet approaches the other. Were it otherwise, there would be a comet every year, for every year there are planets in the same constellation. Again, if the approach of star to star produced a comet, the latter would cease to be in a moment. The transit of stars takes place with the utmost rapidity, thence all eclipse of heavenly bodies is of brief duration; by the same motion they are as swiftly separated as they were brought together. The sun and the moon, as we see, part company within a brief space after the eclipse has begun. How much swifter must be the separation of stars, which are so much smaller? Yet comets last for six months at a time, which would not happen if they sprang from the union of two stars. The stars cannot stick to one another for any long time, and the law of their swift motion must ever drive them asunder. Besides, those stars appear to us to be close to one another, but in reality are separated by immense distances. How, then, could the one star transmit fire to the other so that the two should seem in union, when they are thus parted by an immense tract? The light of the two stars, it is replied, mixes, furnishing the appearance of one. I suppose this means that the phenomenon is much the same as when a cloud takes a ruddy colouring from the rays of the sun striking on it, or as when there is the golden glow of evening or morning, or as when the bow is painted in its varied hues, but only in sunshine.
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Well, my first criticism is that all the instances mentioned are the result of great force. It is the sun that lights them up. The stars do not possess anything like the same power. My second remark is that none of the phenomena arises except below the moon in the vicinity of the earth. The upper regions are pure and spotless, always retaining their own colour. I remark further, that if anything of the kind did occur, it would not last but would speedily disappear, as halos which surround the sun or moon fade in a very brief space of time. Even the rainbow does not long remain. If there was anything of the kind supposed, to unite the space between the two stars, it would disappear with equal rapidity. In any case it would not remain as long as comets are in the habit of doing. The planets have their orbits within the zodiac, they lie near this circle; but comets are seen in all parts of the sky. Their time of appearance is no more certain than the limits of the space which they may not exceed.