The book itself is free on the author's webpage - the reason being the fact that it is not a book per se, but a chapter of a larger work.
A stellar account of Montesquieu's brilliant historical thinking and analitical power. With a lot of quotations from the man himself and without any unfounded criticisms regarding his historical method, is well balanced and enjoyable foray into this first expert in many domains: history, sociology, geography, legal philosophy.