You thought you were making a sound. You were moving water.

Begin with the part that can be measured, because it can be, by anyone with the instrument for it.

When you hum, the air in your nose stops travelling in a straight line and begins to oscillate. That oscillation opens an exchange between the nasal cavity and the sinuses above and behind it — chambers that are otherwise very nearly sealed, and that most people go their whole lives without ventilating on purpose. In 2002 two researchers at the Karolinska Institute in Stockholm put instruments on it and measured what came out.

Not fifteen percent. Fifteen times. From closing your mouth and sounding a note.

Nitric oxide is one of the body’s own signalling molecules — it is made in the sinuses continuously, and it is doing something there, and until 2002 nobody had noticed that a hum is what stirs it. That is not a folk claim and it is not mine. It is in the literature, and I mention it for one reason only: because the oldest practice in the world turns out to have a measurable rim, and the rim is the part a sceptic can check before deciding about the rest.

Now the inside, which is what you actually came for.

You are made mostly of water, and that is where the sound went.

Air carries a tone at about three hundred and forty metres a second. Water carries it more than four times faster, and lets go of it far more slowly. So when you hum with your mouth closed, almost nothing leaves you. The tone goes down into the body’s water and stays there, moving, for as long as you keep sounding — and for a while after you stop, which is the part you felt at the sternum and could not name.

That is why the hum and not the singing voice.

Singing is sound sent out. It is addressed to a room, and it needs one. Humming is sound kept in. It is the only note a human being makes that is addressed to himself, and it is the only one that does not need anybody to receive it.

I have written for thirty years about the three substances of the soul — sound, light and warmth. I set out to write another book about them, and when I read the whole of it back there was water on every page. Rivers, dew, the sea, mist, blood, rain. I had not planned a drop of it. It had come up through the floor of the book the way a spring comes up through a field, without asking my permission.

So I went and stood where it had come up. And what I found is that water is not a fourth thing beside the other three. It is what they move in.

Sound needs a medium or it is nothing — that is not poetry, it is physics; sound is the only one of the three that cannot cross a vacuum. Light will cross empty space. Warmth will radiate across it. Sound will not. Sound must have something to move, and in you, the thing it moves is water.

Which means the soul’s water is not one of the soul’s substances. It is the condition of the others being audible at all.

And a well is not a container of water. It is a place where water that was always underneath is reached.

You did not fill anything this morning. You reached something.