a soft metal washer, which fitted on to this hexagon, and
which would be pressed into the grooves of the rifling, and so spin the
dagger, but would drop off as soon as the weapon left the barrel. Here
is such a washer, which Polton has made for us."
He laid on the table a metal disc, with a hexagonal hole through it.
"This is all very ingenious," said the inspector, "but I say it is
impossible and fantastic."
"It certainly sounds rather improbable," Marchmont agreed.
"We will see," said Thorndyke. "Here is a makeshift cartridge of
Polton's manufacture, containing an eighth charge of smokeless powder
for a 20-bore gun."
He fitted the washer on to the boss of the dagger in the open breech of
the rifle, pushed it into the barrel, inserted the cartridge, and closed
the breech. Then, opening the office-door, he displayed a target of
padded strawboard against the wall.
"The length of the two rooms," said he, "gives us a distance of
thirty-two feet. Will you shut the windows, Jervis?"
I complied, and he then pointed the rifle at the target. There was a
dull report--much less loud than I had expected--and when we looked at
the target, we saw the dagger driven in up to its hilt at the margin of
the bull's-eye.
"You see," said Thorndyke, laying down the rifle, "that the thing is
practicable. Now for the evidence as to the actual occurrence. First, on
the original dagger there are linear scratches which exactly correspond
with the grooves of the rifling. Then there is the fact that the dagger
was certainly spinning from left to right--in the direction of the
rifling, that is--when it entered the body. And then there is this,
which, as you heard, the porter found in the garden."
He opened the paper packet. In it lay a metal disc, perforated by a
hexagonal hole. Stepping into the office, he picked up from the floor
the washer that he had put on the dagger, and laid it on the paper
beside the other. The two discs were identical in size, and the margin
of each was indented with identical markings, corresponding to the
rifling of the barrel.
The inspector gazed at the two discs in silence for a while; then,
looking up at Thorndyke, he said:
"I give in, Doctor. You're right, beyond all doubt; but how you came to
think of it beats me into fits. The only question now is, Who fired the
gun, and why wasn't the report heard?"
"As to the latter," said Thorndyke, "it is probable that he used a
compressed-air attachm
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