  We present a measurement of the composition of B meson inclusive semileptonic
decays using 9.4 fb^-1 of e^+e^- data taken with the CLEO detector at the
Upsilon(4S) resonance. In addition to measuring the charged lepton kinematics,
the neutrino four-vector is inferred using the hermiticity of the detector. We
perform a maximum likelihood fit over the full three-dimensional differential
decay distribution for the fractional contributions from the B -> X_c l nu
processes with X_c = D, D*, D**, and nonresonant X_c, and the process B -> X_u
l nu. From the fit results we extract the first and second moments of the M_X^2
and q^2 distributions with minimum lepton-energy requirements of 1.0 GeV and
1.5 GeV. We find <M_X^2 - M_D[Bar]^2> = 0.456 +- 0.014 +- 0.045 +- 0.109
(GeV/c^2)^2 with a minimum lepton energy of 1.0 GeV and <M_X^2 - M_D[Bar]^2> =
0.293 +- 0.012 +- 0.033 +- 0.048 (GeV/c^2)^2 with minimum lepton energy of 1.5
GeV. The uncertainties are from statistics, detector systematic effects, and
model dependence, respectively. As a test of the HQET and OPE calculations, the
results for the M^X_c moment as a function of the minimum lepton energy
requirement are compared to the predictions.
