Twenty minutes later, in Fritton again, the Inspector produced from a drawer in his desk the magnet he had found in the shrubbery at the Dower House, and bade Sergeant Wake tell him what effect on it an electromagnet would have.
"It would attract it, of course," Wake replied. "Soon as you switched the current on. You mean, somehow or other it was fixed so that when it jumped to the electromagnet, it caught the trigger?"
"Good Lord!" said Cook blankly. "Could that have been done? I never heard of such a thing!"
"What we want to go in for now, is a bit of experiment," said Hemingway. "We'll rig that rifle up in the vice, and see how it could be made to work."
By the time the rifle had been produced, and the vice clamped to the leg of a stout table, Hemingway had discovered an additional reason for the position of the grazes on the sapling. "I get it!" he said. "It had to be close to the ground, to get the trigger on the same level as the electro-magnet. Now, if the two arms of the horseshoe magnet had to point towards the electromagnet, that must have been just behind the trigger, about like that. Come on, Wake! How would you manage to get the horseshoe magnet so that there's nothing to prevent its moving, and so that it's bound to pull that trigger as soon as it does move?"
"Well, it's got to rest on something. Couple of blocks of wood, perhaps."
"That's it," said Hemingway. "Easily kicked away when finished with. Books will be good enough for us. Hand me down a few!"
Kneeling on the floor he carefully built up his two little platforms, one on each side of the trigger-guard of the rifle, and close enough together to allow of the horseshoe magnet's arms resting one on each platform. The magnet he placed so that the round end was within the trigger-guard, and in front of the trigger itself, and the magnetised ends pointing towards the electro-magnet placed under the stock of the rifle. While Sergeant Wake busied himself with a length of flex and a wall-plug, Hemingway tried to cock the rifle. After several abortive attempts, he sat back on his heels and eyed the rifle with dislike. "It's no use: the damned thing won't cock!" he said. "It goes off the moment you close the bolt. Now, how did he work that trick?"
"The bent's been filed down so fine that the searnose won't catch," said' Cook. "I've got a brother in the gun trade, and I've seen these things stripped. The bent was filed down to give it that light pull. He'd have had to load it with the trigger pulled back. Let me try, will you, Inspector? I've got an idea how to cock it."
Hemingway said: "Go right ahead! If you can close the bolt without the blooming thing's going off, you're softer handed than I am."