The lamp-standards were a little difficult to see, and when I heard Rooum
stop suddenly and draw in his breath sharply, I thought he had walked
into one of them. "Hurt yourself?" I said. He walked on without replying; but half a dozen yards farther on he
stopped again. He was listening again. He waited for me to come up. "I say," he said, in an odd sort of voice, "go a yard or two ahead, will
you?" "What's the matter?" I asked, as I passed ahead. He didn't answer. Well, I hadn't been leading for more than a minute before he wanted to
change again. He was breathing very quick and short. "Why, what ails you?" I demanded, stopping. "It's all right.... You're not playing any tricks, are you?..." I saw him pass his hand over his brow. "Come, get on," I said shortly; and we didn't speak again till we struck
the pavement with the lighted lamps. Then I happened to glance at him. "Here," I said brusquely, taking him by the sleeve, "you're not well. We'll call somewhere and get a drink." "Yes," he said, again wiping his brow. "I say ... did you hear?" "Hear what?" "Ah, you didn't ... and, of course, you didn't feel anything...."

"Come, you're shaking." When presently we came to a brightly lighted public-house or hotel, I saw
that he was shaking even worse than I had thought. The shirt-sleeved
barman noticed it too, and watched us curiously. I made Rooum sit down,
and got him some brandy. "What was the matter?" I asked, as I held the glass to his lips. But I could get nothing out of him except that it was "All right--all
right," with his head twitching over his shoulder almost as if he had
touch of the dance. He began to come round a little. He wasn't the kind
of man you'd press for explanations, and presently we set out again. He walked with me as far as my lodgings, refused to come in, but for all
that lingered at the gate as if loath to leave. I watched him turn the
corner in the rain. We came home together again the next evening, but by a different way,
quite half a mile longer. He had waited for me a little pertinaciously. It seemed he wanted to talk about molecules again. Well, when a man of his age--he'd be near fifty--begins to ask questions,
he's rather worse than a child who wants to know where Heaven is or some
such thing--for you can't put him off as you can the child. Somewhere or
other he'd picked up the word "osmosis," and seemed to have some
glimmering of its meaning. He dropped the molecules, and began to ask me
about osmosis. "It means, doesn't it," he demanded, "that liquids will work their way
into one another--through a bladder or something? Say a thick fluid and a
thin: you'll find some of the thick in the thin, and the thin in the
thick?" "Yes. The thick into the thin is ex-osmosis, and the other end-osmosis. That takes place more quickly. But I don't know a deal about it." "Does it ever take place with solids?" he next asked. What was he driving at? I thought; but replied: "I believe that what is
commonly called 'adhesion' is something of the sort, under another name." "A good deal of this bookwork seems to be finding a dozen names for the
same thing," he grunted; and continued to ask his questions. But what it was he really wanted to know I couldn't for the life of me
make out. Well, he was due any time now to disappear again, having worked quite six
weeks in one place; and he disappeared. He disappeared for a good many
weeks. I think it would be about February before I saw or heard of him
again. It was February weather, anyway, and in an echoing enough place that I
found him--the subway of one of the Metropolitan stations. He'd probably
forgotten the echoes when he'd taken the train; but, of course, the
railway folk won't let a man who happens to dislike echoes go wandering
across the metals where he likes. He was twenty yards ahead when I saw him. I recognised him by his patched
head and black hand-bag. I ran along the subway after him. It was very curious. He'd been walking close to the white-tiled wall,
and I saw him suddenly stop; but he didn't turn. He didn't even turn
when I pulled up, close behind him; he put out one hand to the wall, as
if to steady himself. But, the moment I touched his shoulder, he just
dropped--just dropped, half on his knees against the white tiling. The
face he turned round and up to me was transfixed with fright. There were half a hundred people about--a train was just in--and it isn't
a difficult matter in London to get a crowd for much less than a man
crouching terrified against a wall, looking over his shoulder as Rooum
looked, at another man almost as terrified. I felt somebody's hand on
my own arm. Evidently somebody thought I'd knocked Rooum down. The terror went slowly from his face. He stumbled to his feet. I shook
myself free of the man who held me and stepped up to Rooum. "What the devil's all this about?" I demanded, roughly enough. "It's all right ... it's all right,..." he stammered. "Heavens, man, you shouldn't play tricks like that!" "No ... no ... but for the love of God don't do it again!..." "We'll not explain here," I said, still in a good deal of a huff; and
the small crowd melted away--disappointed, I dare say, that it wasn't
a fight. "Now," I said, when we were outside in the crowded street, "you might let
me know what all this is about, and what it is that for the love of
God I'm not to do again." He was half apologetic, but at the same time half blustering, as if I had
committed some sort of an outrage. "A senseless thing like that!" he mumbled to himself. "But there: you
didn't know.... You _don't_ know, do you?... I tell you, d'you hear,
_you're not to run at all when I'm about_! You're a nice fellow and all
that, and get your quantities somewhere near right, if you do go a long
way round to do it--but I'll not answer for myself if you run, d'you
hear?... Putting your hand on a man's shoulder like that, just when ..."

"Certainly I might have spoken," I agreed, a little stiffly. "Of course, you ought to have spoken! Just you see you don't do it again. It's monstrous!" I put a curt question. "Are you sure you're quite right in your head, Rooum?" "Ah," he cried, "don't you think I just fancy it, my lad! Nothing so
easy! I thought you guessed that other time, on the new road ... it's as
plain as a pikestaff... no, no, no! _I_ shall be telling _you_ something
about molecules one of these days!" We walked for a time in silence. Suddenly he asked: "What are you doing now?" "I myself, do you mean? Oh, the firm. A railway job, past Pinner. But we've a big contract coming on in the West End soon they might
want you for. They call it 'alterations,' but it's one of these big
shop-rebuildings." "I'll come along." "Oh, it isn't for a month or two yet." "I don't mean that. I mean I'll come along to Pinner with you now,
to-night, or whenever you go." "Oh!" I said. I don't know that I specially wanted him. It's a little wearing, the
company of a chap like that.