  Skew-symmetric massless fields, their potentials being $r$-forms, are close
analogues of Maxwell's field (though the non-linear cases also should be
considered). We observe that only two of them ($r=$2 and 3) automatically yield
stress-energy tensors characteristic to normal perfect fluids. It is shown that
they naturally describe both non-rotating ($r=2$) and rotating (then a
combination of $r=2$ and $r=3$ fields is indispensable) general relativistic
perfect fluids possessing every type of equations of state. Meanwile, a free
$r=3$ field is completely equivalent to appearance of the cosmological term in
Einstein's equations. Sound waves represent perturbations propagating on the
background of the $r=2$ field. Some exotic properties of these two fields are
outlined.
