ABSTRACT
In the original experiments of Dr. Wood and the writer, the active deposit of thorium was used as a source of radiation, and with the active material available, the α-ray activity of the source of radiation was about 2/100 of a milligram of radium in equilibrium. In order to obtain 20 scintillations a minute, due to the long-range particles, it is necessary that these experiments to place the mica within a few millimetres of the zinc-sulphide screen. It was placed close to the aluminium absorbers, and the microscope so adjusted that, on exciting the magnetic field in one direction, the α- particles fell over the whole surface of the screen and by reversing the field the scintillations were confined to the lower half. Amount of deflexion of the long-range particles by reversing a current through the electromagnet of 6 amps, was directly compared with the deflexion due to the α- rays of range 8.6 cm.
