Lattice gases are investigated consisting of several boxes in which an
y particle interacts only with particles at its nearest neighbour site
s within the same box, and particles can hop from one box to the other
so that the total number is conserved. Two equal square lattices with
attraction between particles in the same plane are simulated using th
e Monte Carlo method. While the equilibrium properties of this system
are related simply to those for the plane, time relaxation differs. Th
ere are some interesting consequences, e.g., a consideration of two la
ttices may permit the more accurate determination of steady state prop
erties in some cases, and novel phenomena may be exhibited. The nature
of finite-size effects for low density is peculiar also. Further case
s that exhibit interesting behaviour, even for one-dimensional boxes,
are studied analytically by means of exact and mean-field solutions.