-particles shot off per second by a small speck of radium or polonium through a given solid angle and computing from this the number of these particles emitted per second by one gram of the radium or polonium. Regener made his determination by counting the scintillations produced on a diamond screen in the focal plane of his observing microscope. He then caught in a condenser all the
-particles emitted per second by a known quantity of his polonium and determined the total quantity of electricity delivered to the condenser by them. This quantity of electricity divided by the number of particles emitted per second gave the charge on each particle. Because the
-particles had been definitely proved to be helium atoms[97] and the value of
found for them showed that if they were helium they ought to carry double the electronic charge, Regener divided his result by 2 and obtained
He estimated his error at 3 per cent. Rutherford and Geiger made their count by letting the