On the exposed top the snow lay thicker, a blanket of white that glittered in the morning sun. All around us hummocks in the snow revealed the presence of burial mounds, each casting a pale lilac shadow in the white. Holmes stood up in the trap and gazed around him.
"Ah! There it is!" he exclaimed, and pointed.
Ahead of us and to our left a dark mark broke the whiteness and, as we moved towards it, we could see that it was another tumulus, bare both of snow and vegetation, exposing raw earth.
"Have you ever photographed the Black Barrow before?" Holmes asked the photographer.
"No, sir. That would be a wasted plate. Nobody hereabouts would pay for a picture of that thing," he replied with some vehemence.
We drew to a halt close to the Black Barrow and Mr Swain set up his camera under Holmes's directions. I walked around the mound, finding it nothing more than a heap of compacted soil, unrelieved by any blade of grass. Its lower edge was ringed with flat stones and, looking closely at its surface, it was possible to see where Sir Andrew's men had cut their trench through its centre. Apart from its nakedness, there was nothing to distinguish it from any of the forty or fifty mounds round about. One did not have to be superstitious to find something disturbing in that patch of dead, dark, soil.
I stepped aside while Mr Swain exposed half a dozen plates and then we were back in the trap and returning to the village.
Holmes was still in good spirits over luncheon, so that I queried his mood. "I have every right to be cheerful, Watson. This morning's excursion gave me the final piece of evidence. Nature has assisted my enquiry, though I made assurance doubly sure and asked Mr Swain for his photographs."
Mr Swain joined us over coffee, rather nervous and apologetic. "I do not know what has happened, Mr Holmes," he said. "The general views of the Moor are crystal clear, as they should have been with this morning's light, but all four plates of the barrow are spoiled. Look," he said and laid the box of plates on the table.
Holmes took each plate in turn and held it up to the window, passing each to me when he had done with it. Two were fine panoramas of the snowclad Moor but each of the others was just a swirl of fog.
"But this is exactly what Edgar said happened to his plates!" I exclaimed.
"Precisely," declared Holmes, "and thereby our case is closed. I am deeply grateful to you, Mr Swain."
The confused photographer took the money that Holmes offered, thanked him and left rapidly, as though he feared my friend would change his mind.
When the coffee was done Holmes drew out his watch. "We might", he said, "catch the mid-afternoon express to London. Would you be so kind as to ask the boy for our bags and the reckoning?"
On the way back to London Holmes discoursed wittily on anarchists and poisoners, on underworld argot and a dozen different topics, but I heard him with only half an ear for my mind was churning in its attempts to make sense of what Sherlock Holmes evidently regarded as a successful enquiry. At length I could stand it no longer.
"Holmes!" I exclaimed, "I have never been so completely at a loss to understand one of your enquiries. What in Heaven's name has this all been about?"
He laughed. "Do you recall", he said, "that when we had not known each other long you took issue with me over my
proposition that, by logical deduction, it should be possible to infer the existence of an ocean from a single grain of sand?" "Well, yes," I said, "but I was not then so familiar with your remarkable methods."
"I fear," he said, "that you are not yet familiar with them. I have been engaged in one of the most enjoyable enquiries that I
can recall, enjoyable because I have had to infer the existence of something which I have never seen and to construct the pattern of its movements and assess its influence by pure reason."
"You have left me a long way behind," I grumbled.
"Consider the patterns, Watson," he said.
"The patterns on the casket?" I asked. "What of them?" "No, Watson," he sighed. "The patterns of the evidence as it unfolded." He leaned forward.
"Let us begin at the beginning. The newspapers told us that snow would not lie and grass would not grow upon the Black
Barrow. I admit I took that for folklore or exaggeration, but you heard Edgar say that it was the case. What did that suggest to you?"
I confessed to no idea at all.
"Watson!" he expostulated. "You have been in mining districts; you have seen heaps of coal waste on which grass will not grow nor the snow lie."
"But that is caused by fires smouldering within the heaps," I said. "Ordinary soil does not smoulder, Holmes."
"No indeed, Watson, but that analogy led me to believe that something within the barrow might be emitting some influence or emanation that warmed its surface yet discouraged growth."
"Such as what?" I asked.
"I admit that, at first, I could see no solution along that line, but then I recalled pitchblende."
"Pitchblende?" I echoed. "What on earth is that?"
"It is an ore, of uranium, found in several places. For centuries German miners have been aware of it and afraid of it, for they
knew that it could cause burns and sickness. Now, you will recall my telling you of my experiments in coal-tar derivatives at the Montpelier laboratories in France, earlier this year?"
"Certainly."
"Among my colleagues there was a French scientist, Jacques Curie, a specialist in electro-magnetism. He introduced me to a remarkable group of people who have theories about that substance. One was a Monsieur Bacquerel, another was Curie's own brother, Pierre, and another was Pierre's assistant and fiancee, a determined and intelligent young Polish lady called Marie Sklodovska. All of them believe that pitchblende emits some influence that can affect its surroundings."
"Good Heavens!" I said. "This sounds more like witch-craft than science."
"I assure you that they are all very fine scientists, Watson, and it occurred to me to proceed on the basis that they are right and that pitchblende, or something like it, had been hidden in that barrow when it was first set up."
He paused. "That would neatly explain our first few facts, but what of the disease? Well, Mr Edgar gave us the answer to that, with his clear proof that the bronze casket had been rifled in the night. Edgar's spoiled photographs were also the proof that something was in the barrow that spoiled his plates. He failed to realise it, but the later success of his photography was also the proof that something had been removed from the mound. He was sadly wrong about Sir Andrew's guilt. It was, of course, the younger Lewis. No doubt, as Edgar described, he waited at the inn for his father's return, and Sir Andrew, fresh from his discovery, would certainly have mentioned it to his son. And so Anthony Lewis robbed the Black Barrow that night as a revenge on his father for refusing to meet his debts, and by so doing he brought about his own death."
"By Jove!" I said, "I begin to see. Everyone who came near was affected in some degree, but he slept with it beneath his bed," and I shuddered at the thought of the luckless youth asleep while the malign emanations that Holmes had described seeped into him hour by hour.
"Exactly, Watson. I told you that we had stumbled upon a crime in our enquiries, but it brought with it its own fearful sentence. Sadly, the presence of that baleful urn at the 'Goat and Boots' was also responsible for the deaths and other effects in the village, though I suppose we should rejoice at the good fortune of Mrs Henty and young Mary. Evidently the influence of the substance is not entirely malign and, if my friends on the Continent, can refine and control it, it may yet prove a blessing."
"If it can destroy a malignant tumour it will be an enormous blessing," I said. "But how came Sir Andrew to die of its effects and why does the snow still not lie on the Black Barrow? Is there more of the stuff still in there?"