"You see," said Templeton in his most earnest manner, "in things like this you can’t do better than follow the example of most other inventors, and see if anything in the natural world will give us a start." "’Follow Nature,’" chuckled Eves. "You remember old Dicky Bird setting that as an essay theme?" "Yes; he sent mine up for good." "He jawed me: sarcastic owl! He was always asking for homely illustrations, as he called them, and when I gave him one he snapped my head off. I wrote, ’An excellent example of the application of this philosophical maxim in practical life is afforded by the navvy, who, as the most casual observer will often have noticed, dispenses with a handkerchief when he has a cold in the head.’ A jolly good sentence, what?" "But I don’t see——" "Oh, it’s not worth explaining; it was the explanation that rattled the Dicky Bird. What were you saying?" "I was saying we ought to get a hint from Nature. What’s the object of the smoke machine?" "To make a deuce of a smother, of course." "Yes, to enable a vessel to hide itself from a submarine. Well, what’s the nearest thing in Nature?" "Give it up; I’m no good at conundrums." "This isn’t a conundrum; it’s a scientific fact. You alarm a cuttle-fish, and it squirts out an inky fluid that conceals it from its enemy." "You don’t say so! Jolly clever of it. Ought to be called the scuttle-fish. But how does that help you? You want your cloud in the air, not in the water." "Of course. The idea is to produce a large volume in a short time, of great opacity, yet spreading rapidly over a large area. What’s the nearest parallel in Nature?" "Human nature?" "I said Nature." "Well, human nature’s a part of Nature; and, if you ask me, I should say a careless cook and a foul kitchen chimney—the fire engine up, and a month’s notice." "I do wish you’d be serious. But you’ve hit it all the same. Half-consumed carbon——" "You mean soot?" "Soot is half-consumed carbon. That’s the stuff we want. It’s the very thing, because a steamship produces loads of it every day. All you want is a suitable apparatus and what you may call a firing charge. I’ll just make a note." He took out his note-book, and wrote in his very neat handwriting the following tabular statement: SMOKE MACHINE. REQUIRED. 1. Soot. 2. Combustibles. 3. Receptacle. 4. Vehicle. "Four-wheelers are cheap, but bang goes your tenner, Bobby," said Eves, looking over his shoulder. "Can’t you do without the vehicle?" "You don’t understand. We must have something to carry the receptacle along at a good speed, like a ship at sea. A motor-boat would be the very thing, but that’s out of the question. We must find something cheap to experiment with on land, and if it works I’ll send the scheme to the Admiralty, and they’ll provide funds for marine tests."