g 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'