  We measured the vertical pressure response function of a layer of sand
submitted to a localized normal force at its surface. We found that this
response profile depends on the way the layer has been prepared: all profiles
show a single centered peak whose width scales with the thickness of the layer,
but a dense packing gives a wider peak than a loose one. We calculate the
prediction of isotropic elastic theory in presence of a bottom boundary and
compare it to the data. We found that the theory gives the right scaling and
the correct qualitative shape, but fails to really fit the data.
