The way I got to know him (got to know him, I mean, more than just to nod) was that he tacked himself on to me one night down Vauxhall way, where we were setting up some small plant or other. We had knocked off for the day, and I was walking in the direction of the bridge when he came up. We walked along together; and we had not gone far before it appeared that his reason for joining me was that he wanted to know "what a molecule was." I stared at him a bit. "What do you want to know that for?" I said. "What does a chap like you, who can do it all backwards, want with molecules?" Oh, he just wanted to know, he said. So, on the way across the bridge, I gave it him more or less from the book--molecular theory and all the rest of it. But, from the childish questions he put, it was plain that he hadn't got the hang of it at all. "Did the molecular theory allow things to pass through one another?" he wanted to know; "_Could_ things pass through one another?" and a lot of ridiculous things like that. I gave it up. "You're a genius in your own way, Rooum," I said finally; "you know these things without the books we plodders have to depend on. If I'd luck like that, I think I should be content with it." But he didn't seem satisfied, though he dropped the matter for that time. But I had his acquaintance, which was more than most of us had. He asked me, rather timidly, if I'd lend him a book or two. I did so, but they didn't seem to contain what he wanted to know, and he soon returned them, without remark. Now you'd expect a fellow to be specially sensitive, one way or another, who can tell when there's water a hundred feet beneath him; and as you know, the big men are squabbling yet about this water-finding business. But, somehow, the water-finding puzzled me less than it did that Rooum should be extraordinarily sensitive to something far commoner and easier to understand--ordinary echoes. He couldn't stand echoes. He'd go a mile round rather than pass a place that he knew had an echo; and if he came on one by chance, sometimes he'd hurry through as quick as he could, and sometimes he'd loiter and listen very intently. I rather joked about this at first, till I found it really distressed him; then, of course, I pretended not to notice. We're all cranky somewhere, and for that matter, I can't touch a spider myself. For the remarkable thing that overtook Rooum--(that, by the way, is an odd way to put it, as you'll see presently; but the words came that way into my head, so let them stand)--for the remarkable thing that overtook Rooum, I don't think I can begin better than with the first time, or very soon after the first time, that I noticed this peculiarity about the echoes.