The Newtonian equation of a circular orbit of an electron rotating about a central attracting charge , at a distance , with a rotational frequency , is The kinetic energy of the electron is . The work required to move the electron from its orbit to a position at rest at infinity is . If we denote this quantity of energy by , it is seen at once that If we combine this with (37), p. 213, there results at once Upon change in orbit the radiated energy must be and, if we place this equal to , there results the Balmer formula (34), p. 210, in which Since for hydrogen , we have and from (60)