“What visitors came to the house?” Patterson asked at length.
“Very few. A youngish gentleman came sometimes. He called the other morning just as I was going out.”
“Who admitted him?”
“The young lady herself.”
Many more questions Patterson put to the old lady, but elicited no noteworthy fact, except that two large, heavy trunks had been sent away by Parcels Delivery a couple of days before. Therefore, thanking Mrs Luff, who, of course, was extremely curious to know why the police were taking such an active interest in her neighbour, we left and made inquiries of the people in the adjoining house on the opposite hand.
It was a lodging-house and the owner, a rather surly old widow, was not at all communicative. What she told us amounted practically to what we had already learnt. She, too, had long ago set the old man and his daughter down as mysterious persons, and her two servants had never been able to find out anything regarding them.
So after nearly half an hour’s absence we returned to the house of mystery, watched, of course, by the persons in the houses on either side. None suspected a tragedy, but all remained at their windows expecting to see somebody arrested.
In the dining-room we found Doctor Knowles, the police divisional surgeon, who had been sent for by the police. He had already examined the bodies and was on the point of returning home.
“Well, doctor, what’s your opinion?” asked Patterson.
“I can form none until after the post-mortem,” answered the prim, youngish, dark-moustached man in silk hat and frock coat, a typical Kensington practitioner, who was known to be a great favourite with his lady patients.
“Are there no marks of violence?”
“None,” he responded. “Although there seems no doubt that there has been foul play, yet the means used to encompass their death remains an entire mystery. That laboratory, too, is a very remarkable feature.”
“Why?” I asked.
“Because the occupant of that place has made a discovery for which scientists have for years striven in vain,” the doctor replied.
“What is it?”
“You noticed those strange globes with the coil of tubing,” he said. “Well, from what I’ve found, it seems that the experimenter has invented a means for the liquefaction of hydrogen in large quantities.”
“Is that anything very remarkable?” I asked, in my ignorance of recent science.
“Remarkable!” he echoed. “I should rather say it was. The discovery will create the greatest interest in the scientific world. Other gases have all been handled as true liquids in measurable quantities, while until now hydrogen has only been seen in clouds or droplets, and never collected into a liquid mass. Upstairs, however, there is actually a glass bowl of liquid hydrogen. The experimenter, whoever he is, has determined at last the exact temperature at which it will liquefy, and thus a field for quite new researches, as also for new generalisations, has been thrown wide open.”
“But why is the discovery so very important?” I asked, still puzzled at the doctor’s unusual enthusiasm.
“Briefly, because by it physicists and chemists can henceforward obtain temperatures lying within thirty-five degrees from the so-called absolute zero of temperature — minus 459 degrees Fahrenheit. A possibility is thus given to study physical bodies in the vicinity of that point, which represents, so to say, the death of matter — that is, absence of the molecular vibrations which we describe as heat.”
This explanation, technical though it was, interested me. I knew Doctor Lees Knowles to be a rising man, and when reporting lectures at the Royal Institution had often noticed him among the audiences. There was no doubt that he was highly excited over the discovery, for, like myself, he had seen the liquid hydrogen boiling without any visible heat. In the papers there had been lots about Professor Dewar’s experiments in the liquefaction of oxygen, fluorine and the newly-discovered helium, and I remembered how all his efforts to bring hydrogen to a liquid state had failed. Now, however, the mysterious occupier of that house had succeeded, and every known gas could now be liquefied.
“But the murder,” observed Patterson, his thoughts reverting to the crime, for to him the most wonderful scientific discovery was as naught. “Can you form absolutely no opinion as to how it was accomplished?”
The doctor shook his head.
“There is nothing whatever to account for their sudden death, as far as I can observe,” he answered. “To the woman, however, death must have come instantly, while the man must have fallen and expired a few seconds later. There seem many mysterious features in the affair.”
“The discoverer of this latest scientific fact is undoubtedly the old man who is absent, the father of the dead girl. From him we may learn something to lead us to form conclusions,” I suggested.
“An old man!” echoed Dr Knowles. “Tell me about him.”
Briefly Patterson related all that had been told us by the neighbours, and when he had finished the doctor exclaimed —
“Then I can tell you one thing which is proved undoubtedly. The old man seen to go in and out was in reality a young one, for while looking over the laboratory I came across a white wig and a make-up box, such as is used by actors. Go upstairs and you’ll find a complete disguise there — broadcloth coat, pepper-and-salt trousers baggy at the knees, old-fashioned white vest, and collars of antique pattern.”
“Surely that can’t be true!” Patterson exclaimed in amazement.
“It certainly is,” the doctor asserted. “Depend upon it that the man lying upstairs dead was the man who has been making these successful experiments, and who for some unknown reason desired to conceal his identity. Recollect that they had few friends, if any, and that their man-servant was a most discreet foreigner, who never gossiped.”
“Then you think that to the world they assumed the position of father and daughter, while in reality they were husband and wife?” I said.
“Most likely,” responded the doctor. “A man to make experiments on an elaborate scale as he has must necessarily have been absorbed in them. Indeed, that apparatus must have taken a year to prepare, and no doubt he has been making constant trials for months. He probably intended to give forth his discovery to the world as a great surprise, but has been prevented from doing so by some extraordinary combination of circumstances which has resulted in his death.”
At that instant we heard a voice in the hall — a quick, sharp voice extremely familiar to me, but nevertheless it caused me to start. Next instant, however, there entered the room the well-known figure of Dick Cleugh.
“Hulloa, old fellow!” he exclaimed, greeting me and taking me aside. “I thought I’d run down and see what’s in this. Funny affair it seems, doesn’t it?”
“Yes,” I answered. “A most remarkable mystery. But why have you come out here?”
“Soon after you left I went to find Lily, but she’s gone into the country. So having nothing else to do I came down to see what had occurred. I knew, of course, from Patterson’s telegram, that it was something unusual.”
“Have you been upstairs?”
“Yes, I’ve been worrying around this last half-hour, while you and Patterson have been making inquiries next door. I’ve been having a look about with the Doctor. It seems that there’s some wonderful apparatus in the laboratory — a discovery for liquefying hydrogen. Has he told you about it?”
“Yes,”