Atomic Physics and Related Subjects.: Communications to Nature.: The Growing Importance of Frequency

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THE relation between energy and mass, e = mc2, where c is numerically the velocity of light, indicates that energy has mass and that mass has energy; furthermore, it suggests that the conservation of mass of the chemists is at one with the conservation of energy of the physicists. This relation appears more emphatic if we so alter the unit, either of mass or of energy, that the constant c2 becomes superfluous, and we write in consequence E = M. This would be correct, for example, if our new unit of energy were 9 × 1020 ergs. We do not therefore state that energy is necessarily matter, but we do state that the same abstract number will express matter in terms of energy, or energy in terms of mass. We must always be careful not to confuse, say, sheep and oxen, because we happen to see the same number of these different animals.

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