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In fact, confusion over units was not confined to electricity and magnetism. When two people spoke of a quantity like 'force' or 'power' you could not be sure that they meant the same thing. James saw a prime opportunity to straighten out the muddle. He went beyond his brief for the paper and proposed a systematic way of defining all physical quantities in terms of mass, length and time, symbolised by the letters M, L and T. For example, velocity was defined L/T, acceleration L/T^2, and force ML/T^2, since, by Newton's second law, force=mass x acceleration. His method is used in exactly this form today. Called dimensional analysis, it seems to us so simple and so natural a part of all physical science that almost nobody wonders who first thought of it.
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