Full Idea
The assumption of permanent substance, which technically underlies the procedure of physics, cannot of course be regarded as metaphysically legitimate.
Gist of Idea
The assumption by physicists of permanent substance is not metaphysically legitimate
Source
Bertrand Russell (The Relation of Sense-Data to Physics [1914], §XI)
Book Reference
Russell,Bertrand: 'Mysticism and Logic' [Unwin 1989], p.162
A Reaction
It is a moot point whether physicists still thought this way after the full arrival of quantum theory in 1926. Russell raises all sorts of nice questions about the relationship between physics and philosophy here. I'm on Russell's side.