  We report novel, high-angular resolution interferometric measurements that
imply the near-infrared nuclear emission in NGC 4151 is unexpectedly compact.
We have observed the nucleus of NGC 4151 at 2.2 microns using the two 10-meter
Keck telescopes as an interferometer and find a marginally resolved source ~0.1
pc in diameter. Our measurements rule out models in which a majority of the K
band nuclear emission is produced on scales larger than this size. The
interpretation of our measurement most consistent with other observations is
that the emission mainly originates directly in the central accretion disk.
This implies that AGN unification models invoking hot, optically thick dust may
not be applicable to NGC 4151.
