Final answer:
The concept of 'simple multiple' refers to the integer multiples of the proton's mass seen in positive ions, crucial for understanding atomic mass. Prior to direct detection, the existence of protons was inferred to account for the remaining positive charge in atoms after electron emission. The discovery of neutrons further explained the mass discrepancy between atomic number and atomic weight.
Step-by-step explanation:
The student's question is about the discovery of the proton and the relative masses of subatomic particles, specifically the concept of 'simple multiple' in relation to the mass of a proton. In the history of particle physics, after the electron was discovered and its properties understood, scientists realized that protons had a mass approximately 1836 times that of an electron. When canal rays, which are streams of positive ions, were observed by Eugene Goldstein, he found that the masses of these positive particles were either equal to the mass of a proton or a simple multiple of it. A 'simple multiple' simply means an integer multiple of the proton's mass, as seen in helium nuclei which have twice the number of protons and four times the mass of hydrogen.
Discovery of the neutron was key to resolving this discrepancy between atomic number and atomic weight. As both a proton and a neutron have similar masses, but the neutron is electrically neutral, this allowed for the correct prediction of the mass of atoms based on their number of protons (atomic number) and neutrons. Notably, the proton was actually inferred to exist by Rutherford before it was directly discovered, because positive charge had to remain after electrons were emitted as cathode rays.