It is a standard fact that the
asymptotic cone O(C) of a convex set C in Rn is the polar of the barrier cone B(C).
In the present note we show that the inner aperture P(C) of C may be obtained from
B(C) in a similar manner. We use this result to study relations between O(C) and
P(C), and to give a short proof of D. G. Larman’s characterization of inner
apertures.