Very little that is new has been contributed to the arrangement of the three radioactive series in the past fifteen years. Recently Gamow and others have pointed out the desirability for a fourth series. Fred Allison and his co-workers have recently examined radioactive matter by a magneto-optical technique and report that they find 90 radioactive electrons and isotopes. These are arranged in four series. Substantial changes are made in arrangements of the three old series, particularly the actinium and the thorium series
