Sir Ernest Rutherford, who succeeded Sir J. J. Thomson as Cavendish Professor of Physics at Cambridge University, was first to recognize that the rays from uranium and radium were not all alike, but consisted of three distinct kinds. In order to distinguish them clearly, without committing himself in advance as to their exact nature, he christened them Alpha, Beta, and Gamma rays--the first three letters of the Greek alphabet. We know now that the Alpha rays are positively charged helium atoms, with two negative electrons missing; that the Beta rays are negatively charged electrons (disembodied “particles” of electricity, exactly like cathode rays); and that the Gamma rays are a type of X-rays, not material particles but merely extremely short magnetic waves or oscillations, akin to ordinary light waves or rays. Dr. R. A. Millikan calls them “the wireless waves of the denizens of the sub-atomic world. They are ether waves, just like light or just like wireless waves, except that the vibration frequency ... amounts to 30 billion billions per second. These are the Gamma rays.” This means that this number of light waves would pass a given point in space each second. Since these rays do not consist of charged particles they are not deflected by electromagnetic or electrostatic fields, as are the Alpha and Beta rays. It has been found that one gram of radium ejects 136,000,000,000 particles a second! The Gamma rays of radium have such penetrating power that a half-inch sheet of lead will reduce their original intensity by only one-half, and they are not absolutely stopped by 20 inches. These invisible light waves, thousands of times shorter than those of visible light, are produced whenever a cathode ray (negative electron) hits matter. Of the atoms forming the substance penetrated, perhaps only one in a billion is struck. It has been said that the Gamma rays (and X-rays) are the result of the back-kick of ejected electrons. Prof. Comstock says that the connection between the Beta rays and the Gamma rays “is probably similar to that between the bullet and the sound in the case of a gun.” However this may be, we know that the Gamma rays are, after all, in essence only excessively minute light waves. While the longest visible light waves are 0.00008 centimeter, the longest Gamma rays are 0.000000013 centimeter; and whereas the shortest visible light waves are 0.00004 centimeter, the shortest Gamma rays are but 0.0000000007 centimeter. The Beta particles are ejected with a velocity of from 90,000 to 160,000 miles a second. Prof. Gustave Le Bon calculated that it would require 340,000 barrels of powder to discharge one bullet at this inconceivable speed! These negatively charged electrons normally revolve around the positively charged nucleus. Under certain conditions, an electron will make 2200 billion revolutions within an atom in one second.