A correspondent, Captain Charles Christie R.E., to whom I have shown these sections after they were printed, objects reasonably enough that commodity… - William Stanley Jevons

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A correspondent, Captain Charles Christie R.E., to whom I have shown these sections after they were printed, objects reasonably enough that commodity should not have been represented by M, or Mass, but by some symbol, for instance Q, which would include quantity of space or time or force, in fact almost any kind of quantity.