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…showed last 75 words of 323 total…red a 15-inch naval shell at a piece of tissue paper and the shell came right back and hit you." From this straightforward observation, Rutherford concluded that the atom's mass must be concentrated in a tiny, positively-charged nucleus, while the electrons occupy the farthest ranges of the atom. Although this planetary model of the atom has been greatly sophisticated over the years, it remains as legitimate today as when it was originally devised by Rutherford.