Falls of meteorites are accompanied in nearly every instance by terrific explosions and sharp reports that can be heard for many miles around, often causing the ground to shake as in an earthquake. The meteorite itself has been described as resembling a ball of fire or the headlight of a locomotive, and is followed frequently by a trail of light or a cloud of smoke. At the time it enters our atmosphere a meteorite is moving with planetary velocity ranging from two to forty-five miles per second. Its interior is intensely cold, approaching in temperature the absolute zero of interplanetary space, and it is, therefore, far more brittle than it would be at ordinary temperatures. As it ploughs its way into the earth's atmosphere its surface temperature is soon raised by friction to at least 3,000° or 4,000° C., which is sufficient to fuse all surface materials into the characteristic black crust, with which stony meteorites are coated.