“How did you get it?” said I.

“I made it.”

I had heard something of Moissan, but I knew his artificial diamonds were very small.  I shook my head.

“You seem to know something of this kind of thing.  I will tell you a little about myself.  Perhaps then you may think better of the purchase.”  He turned round with his back to the river, and put his hands in his pockets.  He sighed.  “I know you will not believe me.”

“Diamonds,” he began—­and as he spoke his voice lost its faint flavour of the tramp and assumed something of the easy tone of an educated man—­“are to be made by throwing carbon out of combination in a suitable flux and under a suitable pressure; the carbon crystallises out, not as black-lead or charcoal-powder, but as small diamonds.  So much has been known to chemists for years, but no one yet has hit upon exactly the right flux in which to melt up the carbon, or exactly the right pressure for the best results.  Consequently the diamonds made by chemists are small and dark, and worthless as jewels.  Now I, you know, have given up my life to this problem—­given my life to it.

“I began to work at the conditions of diamond making when I was seventeen, and now I am thirty-two.  It seemed to me that it might take all the thought and energies of a man for ten years, or twenty years, but, even if it did, the game was still worth the candle.  Suppose one to have at last just hit the right trick, before the secret got out and diamonds became as common as coal, one might realise millions.  Millions!”

He paused and looked for my sympathy.  His eyes shone hungrily.  “To think,” said he, “that I am on the verge of it all, and here!

“I had,” he proceeded, “about a thousand pounds when I was twenty-one, and this, I thought, eked out by a little teaching, would keep my researches going.  A year or two was spent in study, at Berlin chiefly, and then I continued on my own account.  The trouble was the secrecy.  You see, if once I had let out what I was doing, other men might have been spurred on by my belief in the practicability of the idea; and I do not pretend to be such a genius as to have been sure of coming in first, in the case of a race for the discovery.  And you see it was important that if I really meant to make a pile, people should not know it was an artificial process and capable of turning out diamonds by the ton.  So I had to work all alone.  At first I had a little laboratory, but as my resources began to run out I had to conduct my experiments in a wretched unfurnished room in Kentish Town, where I slept at last on a straw mattress on the floor among all my apparatus.  The money simply flowed away.  I grudged myself everything except scientific appliances.  I tried to keep things going by a little teaching, but I am not a very good teacher, and I have no university degree, nor very much education except in chemistry, and I found I had to give a lot of time and labour for precious little money.  But I got nearer and nearer the thing.  Three years ago I settled the problem of the composition of the flux, and got near the pressure by putting this flux of mine and a certain carbon composition into a closed-up gun-barrel, filling up with water, sealing tightly, and heating.”