"The effect on the Earth of a collision with a comet of any size would be negligible, except for possible extensive damage over limited areas," said Dr. S. L. Whipple, Astronomer and supervisor of photography at the Harvard College Observatory, in an interview yesterday.

"The density of the average comet is so small that one can safely regard it as being composed of widely-scattered meteors which, for reasons as yet uncertain, are activated to the point of incandescence when in the neighborhood of the sun. If the earth were to pass through the nucleus of a comet, only a small number of these chunks of matter would hit the Earth, and, at their average velocity of 20 miles per second, the friction of the atmosphere would be sufficient to destroy the smaller chunks entirely, and to diminish the size of the large ones to such an extent that the effect would be largely that of harmless fireworks. However, it is probable that a few large pieces of metal, having diameters as much as a mile long, would reach the Earth and cause considerable damage. As a matter of fact, the atmosphere is the only thing which prevents all kinds and sizes of 'heavenly projectiles' from doing a great deal of harm on the Earth's surface; a grain of sand moving at a speed of 20 miles per second would easily penetrate a human being from head to foot.

"The 'glow' of a falling meteorite is not the result of combustion but of the extreme heat generated during the dissipation of its molecules by swift collision with those of the air. Small deposits of various metals are often found on sandy ocean beds, and it has been conclusively shown that these deposits are collections of single molecules or small particles of metal 'knocked' from meteorites while they moved through the atmosphere."

Dr. Whipple's remarks were occasioned by the recent discoveries of two comets never before observed. Houghton's was first seen at the Cape Observatory in South Africa on April 2.