# Origin of Perron-Frobenius Operator

The Frobenius Perron Operator $P: L^1 \to L^1$ is defined by the integral equation $$\int_A Pf(x) \mu(dx) = \int_{S^{-1}(A)} f(x) \mu(dx)$$ for some $\mu$-non singular map $S$. I found it in the book from 1985 called 'Probabilistic Properties of Deterministic Systems'. But I am not sure who originally invented it. Is there any history known about this subject?