but, in reality, there is no such thing as an exact science. - William Stanley Jevons

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.

Thus monopoly is limited by competition, and no owner, whether of labour, land or capital, can, theoretically speaking,obtain a larger share of produce for it than what other owners of exactly the same kind of property are willing to accept.

A spade may be made of any size, and if the same number of strokes be made in the hour, the requisite exertion will vary nearly as the cube of the length of the blade.