April 20 (UPI) -- On this date in history: In 1871, the U.S. Congress passed the Third Force Act, popularly known as the Ku Klux Klan Act, authorizing President Ulysses S. Grant to declare martial law, impose heavy penalties against terrorist organizations and use military force to suppress the Klan. In 1902, Marie Curie and Pierre Curie isolated radioactive radium salts from the mineral pitchblende in their laboratory in Paris. In 1961, Radio Havana announced that seven members of the group