Proton from different gases had different values of charge-to-mass ratio (e/m), they could not be identified with a single particle, unlike the negative electrons discovered by J. J. Thomson. Wilhelm Wien in 1898 identified the hydrogen ion as particle with highest charge-to-mass ratio in ionized gases. Following the discovery of the atomic nucleus by Ernest Rutherford in 1911, Antonius van den Broek proposed that the place of each element in the periodic table (its atomic number) is equal to its nuclear charge. This was confirmed experimentally by Henry Moseley in 1913 using X-ray spectra. In 1917 (in experiments reported in 1919),
Particle in a box which is proportional to formula_44. The variance in the position is a measure of the uncertainty in position of the particle: The probability density for finding a particle with a given momentum is derived from the wavefunction as formula_46. As with position, the probability density for finding the particle at a given momentum depends upon its state, and is given by where, again, formula_33. The expectation value for the momentum is then calculated to be zero, and the variance in the momentum is calculated to be: The uncertainties in position and momentum (formula_50 and formula_51) are defined as being equal