roducing
myself to him, asked the privilege of visiting his shop next day at
ten. This was accorded with that courtesy which you will always find
among the industrial classes of France, and next day I had the
pleasure of meeting Mr. Edison. During our conversation I complimented
him on his invention of the incandescent electric light, and this was
the reply that has ever remained in my memory:--

'It was not an invention, but a discovery. We knew what we wanted; a
carbonised tissue, which would withstand the electric current in a
vacuum for, say, a thousand hours. If no such tissue existed, then the
incandescent light, as we know it, was not possible. My assistants
started out to find this tissue, and we simply carbonised everything
we could lay our hands on, and ran the current through it in a vacuum.
At last we struck the right thing, as we were bound to do if we kept
on long enough, and if the thing existed. Patience and hard work will
overcome any obstacle.'

This belief has been of great assistance to me in my profession. I
know the idea is prevalent that a detective arrives at his solutions
in a dramatic way through following clues invisible to the ordinary
man. This doubtless frequently happens, but, as a general thing, the
patience and hard work which Mr. Edison commends is a much safer guide.
Very often the following of excellent clues had led me to disaster, as
was the case with my unfortunate attempt to solve the mystery of the
five hundred diamonds.

As I was saying, I never think of the late Lord Chizelrigg without
remembering Mr. Edison at the same time, and yet the two were very
dissimilar. I suppose Lord Chizelrigg was the most useless man that
ever lived, while Edison is the opposite.

One day my servant brought in to me a card on which was engraved 'Lord
Chizelrigg.'

'Show his lordship in,' I said, and there appeared a young man of
perhaps twenty-four or twenty-five, well dressed, and of most charming
manners, who, nevertheless, began his interview by asking a question
such as had never before been addressed to me, and which, if put to a
solicitor, or other professional man, would have been answered with
some indignation. Indeed, I believe it is a written or unwritten law
of the legal profession that the acceptance of such a proposal as
Lord Chizelrigg made to me, would, if proved, result in the disgrace
and ruin of the lawyer.

'Monsieur Valmont,' began Lord Chizelrigg, 'do you ever take up c