The mathematicians and astronomers who have alluded to the effects of a collision between our earth and a comet, have more especially considered the event from a mechanical point of view ; the two bodies were for them simply two projectiles which, both animated with enormous velocities, could not fail to encounter each other with a violence dependent upon their respective masses, velocities, and directions of motion. They foresaw only the dislocation or rupture of two gigantic masses, a catastrophe which would inevitably cause the destruction of the human race, and of all living beings upon the surface of the earth.

Some philosophers, believing a comet to be an incandescent mass, or at least to have become heated to an intense degree during its passage in the near vicinity of the sun, have conceived that it would inevitably set fire to our globe; in which case we should perish both by the shock and by fire

But it was not then possible to view the phenomenon in its true light, since the great principle of the conversion of mechanical energy into heat had not at that time been discovered. Let us therefore continue the same hypothesis of a comet of solid nucleus, of a mass comparable to that of our globe, and coming into collision with the earth from any direction whatever.