  The Lie algebra gl(\lambda) with \lambda \in \mathbb C, introduced by
B.L.Feigin, can be embedded into the Lie algebra of differential operators on
the real line. We give an explicit formula of the embedding of gl(\lambda) into
the algebra D_{\lambda} of differential operators on the space of tensor
densities of degree \lambda on \mathbb R. Our main tool is the notion of
projectively equivariant symbol of a differential operator.
