In a previous letter to NATURE (July 20, 1911, p. 78) the hypothesis was proposed that the atomic weight being equal to about twice the intra-atomic charge, "to each possible intra-atomic charge corresponds a possible element," or that (Physik. Zeitschr, xiv., 1912, p. 39), "if all elements be arranged in order of increasing atomic weights, the number of each element in that series must be equal to its intra-atomic charge."
Charges being known only very roughly (probably correct to 20 per cent.), and the number of the last element Ur [sic] in the series not being equal even approximately to half its atomic weight, either the number of elements in Mendeléeff's system is not correct (that was supposed to be the case in the first letter), or the intra-atomic charge for the elements at the end of the series is much smaller than that deduced from experiment (about 100 for Au).
Now, according to Rutherford, the ratio of the scattering of a particles per atom divided by the square of the charge must be constant. Geiger and Marsden (Phil. Mag., xxv., pp. 617 and 618, notes 1 and 2), putting the nuclear charge proportional to the atomic weight, found values, however, showing, not constancy, but systematic deviation from (mean values) 3.825 for Cu to 3.25 for Au. If now in these values the number M of the place each element occupies in Mendeléeff's series is taken instead of A, the atomic weight, we get a real constant (18.7 ± 0.3); hence the hypothesis proposed holds good for Mendeléeff's series, but the nuclear charge is not equal to half the atomic weight. Should thus the mass of the atom consist for by far the greatest part of a particles, then the nucleus too must contain electrons to compensate this extra charge.
Table of the Ratio of the Scattering per Atom Divided by A^{2} Compared with that Divided by M^{2}
I. | II. | Mean | Mean x 5.4 | Mean x (A^{2} / M^{2}) | M | |
Cu | 3.7 | 3.93 | 3.825 | 20.6 | 18.5 | 29 |
Ag | 3.6 | 3.4 | 3.5 | 18.9 | 18.4 | 47 |
Sn | 3.3 | 3.4 | 3.35 | 18.1 | 19.0 | 50 |
Pt | 3.2 | 3.4 | 3.3 | 17.8 | 18.6 | 82 |
Au | 3.4 | 3.1 | 3.25 | 17.5 | 18.4 | 83 |
Mean | 3.44 | 3.45 | 3.445 | 18.6 | 18.6 |
This paper is cited by Frederick Soddy in his classic paper which introduces the word "isotope." You may go directly to that paper at Carmen Giunta's site.