Roget's Thesaurus

I consider it a loss that most young people today will never have an opportunity to marvel at how intelligently and intuitively Roget constructed his thesaurus. I use, and am grateful for, the on-line one at thesaurus.com, even paying for the privilege to use it all year long, but I was looking at the actual book today and appreciating its creator anew. You can climb into Roget's Thesaurus and get satisfyingly tangled in the threads for hours.