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 2040 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.