But it is known that Lexell's comet was very much demoralized by Jupiter. It first came within the influence of that planet in 1767; it lost its original orbit, and went bobbing around Jupiter until 1779, when it became entangled with Jupiter's moons, and then it lost its orbit again, and was whisked off into infinite space, never more, perhaps, to be seen by human eyes. Is it not reasonable to suppose that an event which thus demoralized the comet may have caused it to cast down a considerable part of its material on the face of Jupiter? Encke's comet revolves around the sun in the short period of twelve hundred and five days, and, strange to say-- "The period of its revolution is _constantly diminishing_; so that, if this progressive diminution always follows the same rate, _the time when the comet_, continually [1. "Edinburgh Review," October, 1874, p. 205.] {p. 86} describing a spiral, _will be plunged into the incandescent mass of the sun can be calculated_."[1] The comet of 1874, first seen by Coggia, at Marseilles, and called by his name, came between the earth and the sun, and _approached within sixty thousand miles of the flaming surface of the sun_. It traveled through this fierce blaze at the rate of _three hundred and sixty-six miles per second!_ Three hundred and sixty-six miles _per second!_ When a railroad-train moves at the rate of a mile per minute, we regard it as extraordinary speed; but three hundred and sixty-six miles _per second!_ The mind fails to grasp it. When this comet was seen by Sir John Herschel, after it had made its grand sweep around the sun, it was not more than _six times the breadth of the sun's face away from the sun_. And it had come careering through infinite space with awful velocity to this close approximation to our great luminary. And remember that these comets are no animalculæ. They are monsters that would reach from the sun to the earth. And when we say that they come so close to the sun as in the above instances, it means peril to the earth by direct contact; to say nothing of the results to our planet by the increased combustion of the run, and the increased heat on earth should one of them fall upon the sun. We have seen, in the last chapter, that the great comet of 1843 possessed a tail one hundred and fifty million miles long; that is, it would reach from the sun to the earth, and have over fifty million miles of tail to spare; and it swept this gigantic appendage around in two hours, describing the are of a circle _six hundred million miles long!_ [1. Guillemin, "The Heavens," p. 247.] {p. 87} The mind fails to grasp these figures. Solar space is hardly large enough for such gyrations. And it must be remembered that this enormous creature actually _grazed the surface of the sun_.