One century after Halley, the French astronomer Laplace, whose mathematical attainments were surpassed only by those of Newton, applied his brilliant mind to the possibility of a collision with a Comet, and arrived at this conclusion:
“The seas would abandon their ancient beds and rush towards the new equator, drowning in one universal deluge the greater part of the human race.... We see, then, in effect, why the ocean has receded from the high lands upon which we find incontestable marks of its sojourn; we see how the animals and plants of the south have been able to exist in the climate of the north, where their remains and imprints have been discovered.”
The famous French mathematician Lalande showed that if a Comet as heavy as the Earth were to come within six times the distance of the Moon, it would exert such a powerful attraction upon the waters of the globe as to pull up a tidal wave 13,000 feet above the ordinary sea-level and inundate the continents Every European mountain would be submerged except Mt. Blanc, and only the inhabitants of the Rockies, the Andes and the Himalayas would escape death.
Since Lalande’s day there has been more than one Comet “scare.” One of these startled Europe in 1832. On October 29th of that year, Biela’s Comet crossed the Earth’s orbit. The announcement was received with stupefaction. It was only when Arago soothingly pointed out that the Earth would not reach the exact point where the Comet had intersected the Earth’s orbit until November 30, at which time the Comet would be 50,000,000 miles away, that the popular excitement subsided. A similar alarm seized the world in 1857. Some prophet declared that on June 13 the world would collide with a certain periodic Comet having a period of revolution of three centuries. It is related that the churches and confessionals were crowded for days. Still another prediction, made in 1872 by Plantamour, the distinguished director of the Geneva Observatory, set Europe in a ferment. His calculations were based on errors, which were pointed out by other astronomers, and the public mind was quieted.
Although more than two centuries have passed since Halley was in his prime, the possibility of a collision with some vagabond star still haunts the mind of the astronomer.
That a collision is apt to occur is an admitted astronomic fact. The latest estimate, made in 1909 by Prof. William H. Pickering of Harvard University, would seem to prove that the core of one Comet in about 100,000,000 Comets will hit the earth squarely. An encounter with some part of a Comet’s head will happen once in 4,000,000 years. Since Comets’ orbit are more thickly distributed near the ecliptic than else where in the celestial sphere, the collisions will occur according to Pickering, perhaps more frequently than this.
Because Pickering’s figures differ from those other astronomers—Arago and Babinet, for instance—it must not be inferred that his predecessors are wrong and that he is right in his calculations. The problem is too complex for that. Pickering, Arago and Babinet differ partly because they have assumed different average sizes for their Comets, and partly because their definitions of visible Comets are not in accord.
That the possibility is very real, we shall all have an opportunity of judging on May 18, 1910. On that date the Earth will be plunged in the tail of Halley’s Comet, and the head will be less than 15,000,000 miles away—a mere hand’s breadth in the vastness of the universe.
What will happen?
Nobody knows for certain.