Almost everything that distinguishes the modern world from earlier centuries is attributable to science, which achieved its most spectacular triumphs in the seventeenth century.

Russell is emphasizing the centrality of scientific method and discovery to the character of modernity. In his view, the decisive break between the premodern and modern worlds is not chiefly political or artistic but epistemic: a new way of knowing that yields reliable, cumulative results. By locating science’s “most spectacular triumphs” in the seventeenth century, he points to the Scientific Revolution (Galileo, Kepler, Newton, and the rise of experimentalism and mathematical physics) as the hinge on which later technological, industrial, and social transformations turned. The claim is also implicitly polemical: it elevates science as the primary engine of progress and invites readers to see modern institutions and everyday life as downstream consequences of that intellectual revolution.