of concentric circles has been happily employed by Professor Bohm-Bawerk.81 Varying his
illustration, let us suppose the circles to be drawn on ground which rises uniformly from the outmost
circle towards the centre O in the accompanying diagram at which the apex tapers to a needle-
point.82 The circles are drawn at equal distances as measured on the surface, and therefore, in a
bird's-eye view which the diagram is intended to represent, become huddled together in the
neighbourhood of the central height. Across the circles, down the hill, flow streams with uniform
velocity, so as to pass from circle to circle in a unit of time. The breadth of a stream increases with
its length,—not in direct proportion to the length, but according to the law of accumulated price.83
The volume of the stream is proportioned to its breadth and to its depth (not shown on the figure).
81. Positive Theory, Book II, chap v.
82. The series of highering circles is not shown in the diagram after the fifth circle.
83. Marshall, as cited above.