Full Idea
In a 'smooth' reduction the laws of the reduced theory (thermodynamics of gases) are pretty much preserved in (and isomorphic with) the corresponding laws in the reducing theory (molecular or kinetic theory of gases).
Clarification
'Isomorphic' means maps onto
Gist of Idea
Smooth reductions preserve high-level laws in the lower level
Source
Frank Jackson (From Metaphysics to Ethics [1998], Ch.3)
Book Reference
Jackson,Frank: 'From Metaphysics to Ethics' [OUP 2000], p.57
A Reaction
Are the 'laws' of weather (e.g. linking humidity, temperature and pressure to rainfall) preserved at the level of physics? One might say that they are not preserved, but they are not lost either (they just fade away). Contradictions would be worrying.