, etc. Since 1 is the smallest whole number, this series should correspond, as indicated heretofore, to the highest frequencies of which hydrogen is capable, the upper limit toward which these frequencies tend being reached when
and
, that is, when
.
Fig. 26—The original Bohr model of the hydrogen atom.
Guided by all of these facts except the last, Niels Bohr, a young mathematical physicist of Copenhagen, in 1913 devised[154] an atomic model which has had some very remarkable successes. This model was originally designed to cover only the simplest possible case of one single electron revolving around a positive nucleus. In order to account for the large number of lines which the spectrum of such a system reveals (see [Fig. 24]), Bohr’s first assumption was that the electron may rotate about the nucleus in a whole series of different orbits, as shown in [Fig. 26], and that each of these orbits is governed by the well-known Newtonian law, which when mathematically stated takes the form: