"That was bad for the Co.," said Carlyle. "Well, the main fact was
plain enough. The heavy train was in the wrong. But was the
engine-driver responsible? He claimed, and he claimed vehemently from
the first, and he never varied one iota, that he had a 'clear'
signal--that is to say, the green light, it being dark. The signalman
concerned was equally dogged that he never pulled off the signal--that
it was at 'danger' when the accident happened and that it had been for
five minutes before. Obviously, they could not both be right."

"Why, Louis?" asked Mr. Carrados smoothly.

"The signal must either have been up or down--red or green."

"Did you ever notice the signals on the Great Northern Railway,
Louis?"

"Not particularly, Why?"

"One winterly day, about the year when you and I were concerned in
being born, the engine-driver of a Scotch express received the 'clear'
from a signal near a little Huntingdon station called Abbots Ripton.
He went on and crashed into a goods train and into the thick of the
smash a down express mowed its way. Thirteen killed and the usual tale
of injured. He was positive that the signal gave him a 'clear'; the
signalman was equally confident that he had never pulled it off the
'danger.' Both were right, and yet the signal was in working order. As
I said, it was a winterly day; it had been snowing hard and the snow
froze and accumulated on the upper edge of the signal arm until its
weight bore it down. That is a fact that no fiction writer dare have
invented, but to this day every signal on the Great Northern pivots