Recent observations strongly indicate that a substantial fraction
of the energy emitted by an AGN is absorbed by nearby optically thick
material, which may be in a flattened distribution orbiting the central
engine. This can account for a) the intrinsically bi-polar structure
seen in many AGNs and b) the apparent differences between AGN types
(e.g. Seyfert 1's & 2's), caused by variations in the viewing angle.
     Detection of this obscuring gas and dust has been one of the
highest priorities in the field, but huge extinction makes it invisible
except in far-IR. Only the very fine SPECTRAL resolution of LWS and SWS
high-resolution FP spectroscopy can provide definitive evidence of
dense, neutral and molecular gas in close orbit around the nucleus. The
low resolution from the grating mode of LWS is certainly inadequate. The
R=1000 provided by SWS at 33um is also insufficient to reliably separate
weak high-velocity wings (or humps) from the stronger but narrower
galactic PDR emission.  Only HIGH SNR FP line profiles can separate the
higher- velocity gas in the torus from other components further out. The
spacing of the red- and blue-shifted peaks will then give a direct
DYNAMICAL measurement of the mass of the central engine.
     Although the LWS will obtain rather short-integration FP profiles
of another [OI] and CO line, there is no guarantee that these will
detect decisively the rotating nuclear disk/torus, because of the very
large uncertainties in its physical parameters (e.g. the wavelength at
which it becomes optically thin). Two of the most promising lines it is
predicted to emit strongly, [OI]145um and CO (J=81-->80), are not
being observed at high resolution in the Core Program. Given the great
scientific importance of the result, more than one possible torus
emission line should be studied in detail. If more than one is detected,
additional torus physics can be determined. To search for the torus
predicted in BOTH Seyfert 1 and 2 nuclei, we propose to observe these
lines in by far the brightest example of each class: NGC4151 & NGC1068.