In this Part of this Act—
the expression " dust " does not include dust emitted from a chimney as an ingredient of smoke;
the expression " smoke " includes soot, ash, grit and gritty particles; and
the expression " chimney " includes structures and openings of any kind from or through which smoke may be emitted.
In determining for the purposes of this Part of this Act whether the best practicable means have been taken for preventing, or for counteracting the effect of, a nuisance, a court shall have regard to cost and to local conditions and circumstances.