The planet Mars revolves about the Sun at the rate of 24,000 meters per second. At this distance the comet’s velocity is 34,000 meters per second.
The mean velocity of the Earth in its orbit is 29,460 meters per second, a little less in June, a little more in December. In the neighborhood of the Earth, therefore, the velocity of the comet is 41,660 meters, independently of the acceleration which the Earth might occasion.
These facts the laureate of the Institute called to the attention of the public which, moreover, already possessed some general notions upon the theory of celestial mechanics.
When the threatening star arrived at a distance from the Sun equal to that of Mars, the popular fear was no longer a vague apprehension; it took definite form, based, as it was, upon the exact knowledge of the comet’s rate of approach. Thirty-four thousand meters per second meant 2,040 kilometers per minute, or 122,400 kilometers per hour!
As the distance of the orbit of Mars from that of the Earth is only 76,000,000 of kilometers, at the rate of 122,400 kilometers an hour, this distance would be covered in 621 hours, or about twenty-six days. But, as the comet approached the Sun, its velocity would increase, since at the distance of the Earth its velocity would be 41,660 meters per second. In virtue of this increase of speed, the distance between the two orbits would be traversed by a comet in 558 hours, or in twenty-three days, six hours.
But the Earth at the moment of meeting with the comet, would not be exactly at that point of its orbit intersected by a line from the comet to the Sun, because the former was not advancing directly toward the latter; the collision, therefore, would not take place for nearly a week later, namely: at about midnight on Friday, the 13th of July. It is unnecessary to add that under such circumstances the usual arrangements for the celebration of the national fête of July 14th had been forgotten. National fête! No one thought of it. Was not that date far more likely to mark the universal doom of men and things? As to that, the celebration by the French of the anniversary of that famous day had lasted—with some exceptions, it is true—for more than five centuries: even among the Romans anniversaries had never been observed for so long a period, and it was generally agreed that the 14th of July had outlived its usefulness.
It was now Monday, the 8th of July. For five days the sky had been perfectly clear, and every night the fan-like comet hovered in the sky depths, its head, or nucleus, distinctly visible and dotted with luminous points which might well be solid bodies several kilometers in diameter, and which, according to the calculations, would be the first to strike the Earth, the tail being in a direction away from the Sun and in the present instance behind and obliquely situated with reference to the direction of motion. The new star blazed in the constellation of Pisces. According to observations taken on the preceding evening, July 8th, its exact position was: right ascension, 23 h. 10 m. 32 s.; declination north, 7° 36′ 4″. The tail lay entirely across the constellation of Pegasus. The comet rose at 9 h. 49 m. and was visible all night long.
During the lull of which we have spoken, a change in public opinion had occurred. From a series of retrospective calculations an astronomer had proved that the Earth had already on several occasions encountered comets, and that each time the only result had been a harmless shower of shooting stars. But one of his colleagues had replied that the present comet could not in any sense be compared to a swarm of meteors, that it was gaseous, with a nucleus composed of solid bodies and he had in this connection recalled the observations made upon a comet famous in history, that of .
This comet of justified, in a certain respect, a real apprehension. Its dimensions were recalled to mind: its length of 180,000,000 kilometers, that is to say, a distance greater than that of the Earth from the Sun; and the width of its tail at its extreme point, 24,000,000 kilometers. The diameter of its nucleus measured 1,800,000 kilometers, forty thousand times that of the Earth, and its nebulous and remarkably regular elliptical head was a spot brilliant as a star, having itself a diameter of no less than 200,000 kilometers. The spot appeared to be of great density. It was observed for sixteen months and twenty-two days. But the most remarkable feature of this comet was the immense development to which it attained without approaching very close to the Sun; for it did not reach a point nearer than 150,000,000 kilometers, and thus remained more than 170,000,000 kilometers from the Earth. As the size of comets increases as they near the Sun, if this one had experienced to a greater degree the solar action, its appearance would certainly have been still more wonderful, and, doubtless, terrifying to the observer. And as its mass was far from insignificant, if it had fallen directly into the Sun, its velocity, accelerated to the rate of five or six hundred thousand meters per second at the moment of collision, might, by the transformation of mechanical energy into thermal energy, have suddenly increased the solar radiations to such a degree
