Radio-activity

—That property of a substance by which it spontaneously emits rays which affect a sensitive photog rap hie plate, excite phosphorescence in certain substances, and ionize the surrounding air, that is to say, break up the molecules of the air into atoms which become electrical conductors. Evidence shows that radio-activity is a general property of all matter in a higher or lower degree, instead of its being confined to a few extremely rare substances. The phenomena of emi ion of various minute corpuscles accompanies the breaking up of a supposedly irreducible atom into simpler forms, and observation of these manifestations is altering or modifying the physical conceptions of matter,