  We consider the gedanken calculation of the pair correlation function of
spatially-separated macroscopic string solitons in strongly coupled type IIA
string/M theory, with the macroscopic strings wrapping the eleventh dimension.
The supergravity limit of this correlation function with well-separated,
pointlike macroscopic strings corresponds to having also taken the IIA string
coupling constant to zero. Thus, the pointlike limit of the gedanken
correlation function can be given a precise worldsheet description in the 10D
weakly-coupled type IIA string theory, analysed by us in hep-th/0007056 [Nucl.
Phys. B591 (2000) 243]. The requisite type IIA string amplitude is the
supersymmetric extension of the worldsheet formulation of an off-shell closed
string tree propagator in bosonic string theory, a 1986 analysis due to Cohen,
Moore, Nelson, and Polchinski. We point out that the evidence for pointlike
sources of the zero-form field strength provided by our worldsheet results
clarifies that the electric-magnetic duality in the Dirichlet-brane spectrum of
type II string theories is eleven-dimensional.
