Geometric Proofs of Some Results of Morita

Abstract

In this note we give geometric formulations and proofs of three results of S. Morita. These results relate certain two dimensional cohomology classes of various moduli spaces of curves. We also give a geometric interpretation of a fourth result of Morita. One motivation of this work is to facilitate the application of these results in our work (in preparation) on the Arakelov geometry of moduli spaces of curves.

Latex2e, 15 pages. In this revised version, the statements of the main results remain the same, but one proof has been clarified and improved