Bearing his candle aloft, he led us down the cold passage-way to the laboratory. Those few seconds are vivid in my memory: the light of the candle casting huge shadows from Moses’s wide skull, and his jacket and boots glimmering in the uncertain light; behind me the Morlock’s feet padded softly, and in the enclosed space his rotten-sweet stench was strong.

At the laboratory Moses made his way around the walls and benches, lighting candles and incandescent lamps. Soon the place was brightly lit. The walls were whitewashed and free of ornamentation — save for some of Moses’s notes, crudely pinned there — and the single book-case was crammed with journals, standard texts and volumes of mathematical tables and physical measurements. The place was cold; in my shirtsleeves, I found myself shivering, and wrapped my arms about my body.

Nebogipfel padded across the workshop floor towards the book-case. He crouched down and studied the battered spines of the volumes there. I wondered if he could read English; for I had seen no evidence of books or papers in the Sphere, and the lettering on those ubiquitous panels of blue glass had been unfamiliar.

“I’m not very interested in giving you a biographical summary,” Moses said. “And nor” — more sharply — “do I understand yet why you are so interested in me. But I’m willing to play your game. Look here: suppose I run you through my most recent experimental findings. How does that sound?”

I smiled. How in keeping with my — his — character, with little at the surface of the mind but the current puzzle!

He went to a bench, on which stood a haphazard arrangement of retort stands, lamps, gratings and lenses. “I’d be grateful if you wouldn’t touch anything here. It may look a little random, but I assure you there’s a system! I have the devil of a time keeping Mrs. Penforth and her dusters and brooms out of here, I can tell you.”

Mrs. Penforth? I had an impulse to ask after Mrs. Watchets — but then I remembered that Mrs. Penforth had been Mrs. Watchets’s predecessor. I had released her some fifteen years before my departure into time, after I had caught her pilfering from my small stock of industrial diamonds. I thought of warning Moses of this little occurrence, but no real harm had been done; and — I thought with an oddly paternal mood towards my younger self — it would probably do Moses good to take a closer interest in the affairs of his household for once in a while, and not leave it all to chance!

Moses went on, “My general field is physical optics — that is to say, the physical properties of light, which—”

“We know,” I said gently.

He frowned. “All right. Well, recently, I’ve been somewhat diverted by an odd conundrum — it’s the study of a new mineral, a sample of which I came upon by chance two years ago.” He showed me a common eight-ounce graduated medicine bottle, plugged with rubber; the bottle was half-full of a fine, greenish powder, oddly shining. “Look here: can you see how there is a faint translucence about it, as if it were glowing from within?” And indeed the material shone as if it were composed of fine glass beads. “But where,” Moses went on, “is the energy source for such illumination?

“So I began my researches — at first in odd moments, for I have my work to do! — I depend on grants and commissions, which depend in turn on my building up a respectable flow of research results. I have no time for chasing wild geese… But later,” he admitted, “this Plattnerite came to absorb a great deal of my times — for such I had decided to call the stuff, after the rather mysterious chap — Gottfried Plattner, he called himself — who donated it to me.

“I’m no chemist — even within the limits of the Three Gases my practical chemistry has always been a little tentative — but still, I set to with a will. I bought test tubes, a gas supply and burners, litmus paper, and all the rest of that smelly paraphernalia. I poured my green dust into test tubes and tried it with water, and with acids — sulphuric, nitric and hydrochloric — learning nothing. Then I emptied out a heap onto a slate and held it over my gas burner.” He rubbed his nose. “The resulting bang blew out a skylight and made a fearful mess of one wall,” he said.

It had been the south-western wall which had sustained damage, and now — I could not help myself — I glanced that way, but there was nothing to distinguish it, for the repair work had been thorough. Moses noted my glance, curiously, for he had not indicated which wall it had been.

“After this failure,” he went on, “I was still no closer to unraveling the mysteries of Plattnerite. Then, however” — his tone grew more animated — “I began to apply a little more reason to the case. The translucence is an optical phenomenon, after all. So — I reasoned — perhaps the key to the secrets of Plattnerite lay not in its chemistry, but in its optical properties.”

I felt a peculiar satisfaction — a kind of remote self-regard — at hearing this summary of my own clear thinking processes! And I could tell that Moses was enjoying the momentum of his own narrative: I have always enjoyed recounting a good tale, to whatever audience — I think there is something of the showman in me.

“So I swept aside my clutter of Schoolboy Chemistry,” Moses went on, “and began a new series of tests. And very quickly I came upon striking anomalies: bizarre results concerning Plattnerite’s refractive index — which, you may know, depends on the velocity of light within the substance. And it turned out that the behavior of light rays passing through Plattnerite is highly peculiar.” He turned to the experiment on the bench-top. “Now, look here; this is the clearest demonstration of Plattnerite’s optical oddities which I have been able to devise.”

Moses had set up his test in three parts, in a line. There was a small electric lamp with a curved mirror behind it, and, perhaps a yard away, a white screen, held upright by a retort stand; between these two, clamped in the claws of another retort, was a cardboard panel which bore the evidence of fine scoring. Beside the lamp, wires trailed to an electromotive cell beneath the bench.

The set-up was lucidly simple: I have always sought as straightforward as possible a demonstration of any new phenomenon, the better to focus the mind on the phenomenon itself, and not on deficiencies in the experimental arrangement, or — it is always possible — some trickery on behalf of the experimenter.

Now Moses closed a switch, and the lamp lit; it was a small yellow star in the candle-lit room. The cardboard panel shielded the screen from the light, save for a dim central glow, cast by rays admitted by the scoring in the panel. “Sodium light,” Moses said. “It is nearly a pure color — as opposed, say, to white sunlight, which is a mixture of all the colors. This mirror behind the lamp is parabolic, so it casts all the lamp’s light towards the interposed card.”

He traced the paths of the light rays towards the card. “On the card I have scored two slits. The slits are a mere fraction of an inch apart — but the structure of light is so fine that the slits are, nevertheless, some three hundred wavelengths apart. Rays emerge from the two slits” — his finger continued on “and travel onwards to the screen, here. Now, the rays from the two slits interfere — their crests and troughs reinforce and cancel each other out, at successive places.” He looked at me uncertainly. “Are you familiar with the idea? You would get much the same effect if you were to drop two stones into a still pond, and watch how the spreading ripples coalesced…”

“I understand.”

“Well, in just the same way, these waves of light — ripples in the ether — interfere with each other, and set up a pattern which one may observe, here on this screen beyond.” He pointed to the patch of yellow illumination which had reached the screen beyond the slits. “Can you see? — one really needs a glass — right at the heart of it, there, you’ll see bands of illumination and darkness, alternating, a few tenths of an inch apart. Well, those are the spots where the rays from the two slits are combining.”