  The relativistic generalization of the Chaplygin gas, put forward by Jackiw
and Polychronakos, is derived in Duval's Kaluza-Klein framework, using a
universal quadratic Lagrangian. Our framework yields a simplified proof of the
field-dependent Poincar\'e symmetry Our action is related to the usual
Nambu-Goto action [world volume] of $d$-branes in the same way as the Polyakov
and the Nambu action are in strings theory.
