Cleek motioned to a chair.
"Better sit down to it, my young friend," he said, gently. "Because, to one who isn't interested, it is an extremely dull subject. However, it is better that you should know—as you don't seem to have learnt it at school. Here goes: marsh gas, or methane as it is sometimes called, is the first of the group of hydrocarbons known as paraffins. Whether that conveys anything to you I don't know. But you've asked for knowledge and I mean you to have it." He smiled again, and Merriton gravely shook his head, while Mr. Narkom, dropping for the time being his air of pompous boredom, became the interested listener in every line of his ample proportions.
"Go on, old chap," he said eagerly.
"Methane," said Cleek, serenely, "is a colourless, absolutely odourless gas, slightly soluble in water. It burns with a yellowish flame—which golden tinge you have no doubt noticed in these famous flames of yours—with the production of carbonic acid and water. In the neighbourhood of oil wells in America, and also in the Caucasus, if my memory doesn't fail me, the gas escapes from the earth, and in some districts—particularly in Baku—it has actually been burning for years as sacred fires. A question of atmosphere and education, you see, Sir Nigel."
"Good Heavens! Then you mean to say that those beastly things out there are not lit by any human or superhuman agency at all!" exploded Merriton at this juncture. "And that they have nothing whatever to do with the vanishing of Wynne and Collins?"
Cleek shook his head emphatically.
"Pardon me," he said, "but I didn't say that. The first part of the sentence I agree with entirely. Those so-called flames are lit only by the hand of the Infinite. And the Infinite is always mysterious, Sir Nigel. But as to whether they have any bearing upon the disappearances of those two men is a horse of another colour. We'll look into that later on. In coal-mines marsh gas is considered highly dangerous, and the miners call it fire-damp. But that is by the way. What enters into the immediate question is the fact that there is a patch of charred grass upon the Fens where you say the vanished man, Dacre Wynne's footprints suddenly ended. Hmm."
He stopped speaking suddenly, and getting up again crossed over to the window. He stood for a moment looking out of it, his brows drawn down, his face set in the stern lines that betokened concentration of thought.
Mr. Narkom and Merriton watched him with something of wonder in their eyes. To Merriton, at any rate, who really knew so little of Cleek's unique and powerful mind, the fact of a policeman having such extensive information was surprising in the extreme.
"You don't think, then," he said, breaking the silence that had fallen upon them, "that this—er—marsh gas could have caused the death of Wynne and Collins? Burnt 'em alive, so to speak?"