ction than the
prospect of a night ride on the Scotch express, and the view from the
windows of the train as it passes through the northern part of London
is particularly conducive to thoughts of annihilation.'

'What became of the weapon?'

'That is just the point on which I wish to satisfy myself. Excuse me
for a moment.'

Mr. Sherlaw Kombs drew down the window on the right hand side, and
examined the top of the casing minutely with a magnifying glass.
Presently he heaved a sigh of relief, and drew up the sash.

'Just as I expected,' he remarked, speaking more to himself than to
me. 'There is a slight dent on the top of the window-frame. It is of
such a nature as to be made only by the trigger of a pistol falling
from the nerveless hand of a suicide. He intended to throw the weapon
far out of the window, but had not the strength. It might have fallen
into the carriage. As a matter of fact, it bounced away from the line
and lies among the grass about ten feet six inches from the outside
rail. The only question that now remains is where the deed was
committed, and the exact present position of the pistol reckoned in
miles from London, but that, fortunately, is too simple to even need
explanation.'

'Great heavens, Sherlaw!' I cried. 'How can you call that simple? It
seems to me impossible to compute.'

We were now flying over Northern London, and the great detective
leaned back with every sign of _ennui_, closing his eyes. At last he
spoke wearily:

'It is really too elementary, Whatson, but I am always willing to
oblige a friend. I shall be relieved, however, when you are able to
work out the ABC of detection for yourself, although I shall never
object to helping you with the words of more than three syllables.
Having made up his mind to commit suicide, Kipson naturally intended
to do it before he reached Brewster, because tickets are again
examined at that point. When the train began to stop at the signal
near Pegram, he came to the false conclusion that it was stopping at
Brewster. The fact that the shot was not heard is accounted for by the
screech of the air-brake, added to the noise of the train. Probably
the whistle was also sounding at the same moment. The train being a
fast express would stop as near the signal as possible. The air-brake
will stop a train in twice its own length. Call it three times in this
case. Very well. At three times the length of this train from the
signal-post towards London, d