But when Charlotte could spare any time she gave me considerable help in what I was trying to do.  One great service she was rendering has already been made clear:  she wore the ring constantly, thus relieving me of the anxiety of caring for it.  I was very cautious not to have it in my possession for more than a few minutes at a time.

My first move was to set down, in orderly fashion, the list of the gem’s attributes.  I grouped together the fluctuating nature of its pale blue colour, its power of reproducing those who had gone into the Blind Spot, its combination of perfect solidity with extreme lightness; its quality of coldness to the touch of a male, and warmth to that of a female; and finally its ability to induct—­I think this is the right term—­to induct sounds out of the unknown.  This last quality might be called spasmodic or accidental, whereas the others were permanent and constant.

Now, to this list I presently was able to add that the gem possessed no radioactive properties that I could detect with the usual means.  It was only when I began dabbling in chemistry that I learned things.

By placing the gem inside a glass bell, and exhausting as much air as possible from around it, the way was cleared for introducing other forms of gases.  Whereupon I discovered this: 

The stone will absorb any given quantity of hydrogen gas.

In this respect it behaves analogously to that curious place on the door-frame.  Only, it absorbs gas, no liquid; and not any gas, either—­none but hydrogen.

Now, obviously this gem cannot truly absorb so much material, in the sense of retaining it as well.  The simple test of weighing it afterwards proves this; for its weight remains the same in any circumstances.

Moreover, unlike the liquids which I poured into the wood and saw afterwards in the basement, the gas does not escape back into the air.  I kept it under the Dell long enough to be sure of that.  No; that hydrogen is, manifestly, translated into the Blind Spot.

Learning nothing further about the gem at that time, I proceeded to investigate the trim of the door.  I began by trying to find out the precise thickness of that liquid-absorbing layer.

To do this I scraped off the “skin” of the air-darkened wood.  This layer was .02 of an inch thick.  And—­that was the total amount of the active material!

I put these scrapings through a long list of experiments.  They told me nothing valuable.  I learned only one detail worth mentioning; if a fragment of the scrapings be brought near to the Holcomb gem—­say, to within two inches—­the scrapings will burst into flame.  It is merely a bright, pinkish flare, like that made by smokeless rifle-powder.  No ashes remain.  After that we took care not to bring the ring near the remaining material on the board.

All this occurred on the first day after Ariadne was stricken.  Jerome phoned to say that he had engaged the services of a dozen private detectives, and expected to get wind of the Rhamda any hour.  Both Dr. Hansen and Dr. Higgins called twice, without being able to detect any change for the better or otherwise in their patient.