Note 38 — Chapter IX · CATHODE RAYS AND RADIOACTIVE BODIES
Reading edition
An actinium X was also discovered by Professor Giesel (Jahrbuch d. Radioaktivitat, i. p. 358, 1904). Since the above was written, another product has been found to intervene between the X substance and the emanation in the case of actinium and thorium. They have been named radio-actinium and radio-thorium respectively.—ED.