Roget's International Thesaurus was not designed to be read. It's wonderful for browsing, though.
The real charm to it is that it is organized by topic, not alphabetically. You can drill down from the overarching concepts or look up the section in the index in the back. But once you have gotten to it -- well, in an alphabetical one, since they have to repeat the synonyms for each word, they have to limit their size. For this one, under "Light" they have nearly two pages covering nouns -- shine, glitter, flash, daylight, iridescence -- verbs -- shine, luminesce, illuminate -- and adjectives -- bright, flashing, illuminating -- each of which words is beginning of a paragraph of closely related words, among many such clumps.
It's not a book for reading, but anyone in love with words will find it a nice book for browsing.