  In the 80's M. Cornalba and J. Harris discovered a relation among the Hodge
class and the boundary classes in the Picard group with rational coefficients
of the moduli space of stable, hyperelliptic curves. They proved the relation
by computing degrees of the classes involved for suitable one-parameter
families. In the present article we show that their relation can be obtained as
the class of an appropriate, geometrically meaningful empty set, thus
conforming with C. Faber's general philosophy to finding relations among
tautological classes in the Chow ring of the moduli space of curves. The empty
set we consider is the closure of the locus of smooth, hyperelliptic curves
having a special ramification point.
