We re-examine the use of the energy principle as applied to the tearin
g instability in the magnetotail. We demonstrate that when a magnetic
field component normal to the current sheet is present, electron pitch
-angle diffusion (PAD) either by micro-turbulence or by chaotic orbits
cannot remove the strong stabilization of the tearing mode caused by
electron compressibility. We find that our conclusions are in agreemen
t with those of Pellat et al. [1991], who argued on the basis of canon
ical Py conservation that the stabilization of the ion tearing mode ca
nnot be removed by the introduction of PAD. Our results are at varianc
e with those of Kuznetsova and Zelenyi [1991], who argued that the app
lication of the energy principle used by Pellat et al. [1991] is incor
rect, and that tearing is in fact unstable in the limit of strong PAD.
We show that the disagreement between these two studies can be traced
to an incorrect orbit evaluation first introduced by Coroniti [1980]
and subsequently used by Kuznetsova and Zelenyi [1991].