Empirical and Lyrical (Which makes it… Emplyrical?)
When we say that Victor Hugo's tone is empirical, it means that he backs up everything he tells us about his characters with evidence. When he has no evidence to give, he makes no judgment, which is not a bad strategy to use on our own judgments on other people. Whenever we say a person is this or that, we should be able to give specific examples and hard evidence. When speaking of Bishop Myriel, for example, Hugo writes:
Amid the distractions and frivolities that occupied his life, did it happen that he was suddenly overtaken by one of those mysterious and awful revulsions which, striking to the heart, change the nature of a man who cannot be broken by outward disasters affecting his life and fortune? No one can say. All that is known is that when he returned from Italy he was a priest. (126.96.36.199)
As you can see from his passage, Hugo is constantly making us aware of how limited our knowledge of other people really is. Yes, our brains are usually tempted to jump to conclusions because we like to think we can size people up immediately. But when you actually hold yourself to hard evidence, you realize how little you can actually back up.
Now usually, you'd expect an empirical tone to sound scientific and rational. But Hugo does a great job of blending poetic and descriptive language with his empirical approach to characters. And when you get both together, you get a super rich style.