What is the author's tone in Russian Thinkers by Isaiah Berlin?

Berlin's tone is serious, yet playful and detached. He assumes what, to today's readers, may look like a great deal of knowledge about Russian society and writers, but it was was in fact what most listeners at a public lecture would have known in the mid-twentieth century, concerned as it was with the origins and threat of Soviet Communism. Berlin's tone resembles that of Alexander Herzen, whose thought Berlin evidently admires. Berlin describes Herzen as a witty conversationalist and a sometime malicious observer of his friends. But he most admires Herzen's refusal to accept the illusions and pseudo-certainties of the "new men," violent revolutionaries impatient with talk and analysis. Like Turgenev, Berlin has a gift for entering into the views and sympathies of those with whom he may not agree, so that whole paragraphs of his essays paraphrase writings from the mid-nineteenth-century. Part of the reason why Berlin does this, of course, is that there were no English translations of some of the materials Berlin was quoting or paraphrasing.