But a fall of meteoric stones that chanced upon the department of Orne, France, in 1805, led to a critical investigation by Biot, the distinguished physicist and academician. According to his report a violent explosion in the neighborhood of L'Aigle had been heard for a distance of seventy-five miles around, and lasting five or six minutes, about 1 P. M. on Tuesday, April 26. From several adjoining towns a rapidly moving fireball had been seen in a sky generally clear, and there was absolutely no room for doubt that on the same day many stones fell in the neighborhood of L'Aigle. Biot estimated their number between two and three thousand, and they were scattered over an elliptical area more than six miles long, and two and a half miles broad. Thenceforward the descent of meteoric matter from outer space upon the earth has been recognized as an unquestioned fact. The origin of these bodies being cosmic, meteors may be expected to fall upon the earth without reference to latitude, or season, or day and night, or weather. On entering our upper atmosphere their temperature must be that of space, many hundred degrees below zero; and their velocities range from ten miles per second upward. But atmospheric resistance to their flight is so great that their velocity is quickly reduced: at ground impact it does not exceed a few hundred feet per second. On January 1, 1869, several meteoric stones fell on ice only a few inches thick in Sweden, rebounding without either breaking through the ice or being themselves fractured. Naturally the flight of a meteor through the atmosphere will be only a few seconds in duration, and owing to the sudden reduction of velocity, it will continue to be luminous throughout only the upper part of its course. Visibility generally begins at an elevation of about seventy miles, and ends at perhaps half that altitude. What is the origin of meteors? Theories there are in great abundance: that they come from the sun, that they come from the moon, that they come from the earth in past ages as a result of volcanic action, and so on. But there are many difficulties in the way of acceptance of these and several other theories. That all meteors were originally parts of cometary masses is however a theory that may be accepted without much hesitation.