Full Idea
It is not in the sameness of causes and effects that the constancy of scientific law consists, but in sameness of relations. And even 'sameness of relations' is too simple a phrase; 'sameness of differential equations' is the only correct phrase.
Gist of Idea
The constancy of scientific laws rests on differential equations, not on cause and effect
Source
Bertrand Russell (On the Notion of Cause [1912], p.186)
Book Reference
Russell,Bertrand: 'Mysticism and Logic' [Unwin 1989], p.186
A Reaction
This seems to be a commitment to the regularity view, since there is nothing more to natural law than that the variables keeping obeying the equations. It also seems to be a very instrumentalist view.