ABSTRACT
All the radioactive substances possess in common the power of acting on a photographic plate and of ionizing the gas in their immediate neighbourhood. The intensity of the radiations may be compared by means of the photographic or electrical action; and in the case of the strongly radioactive substances by the power of lighting up a fluorescent screen. The radiating power of the emanation rapidly diminishes, falling to half its value in about one minute. Becquerel has examined the rays of uranium in a magnetic field by the photographic method, and found that some of them are deflectable. The rays not acted on by a magnetic field can be distinguished from each other by their power of penetrating through thin layers of metal, and their absorption in gases. The relative ionization of hydrogen compared with that of air and other gases is quite different for the deviable and non-deviable rays of radioactive substance.
