He sort of... drifts... slowly to his knees, staring.
(The first book he ever printed with his own hands, complete with stray inky thumbprint on the cover. Jim's favorite necktie, with Peg's slightly askew little embroidered fish along the edges. The wooden rosary his mother carved him for his first communion. The hand-painted locket portrait of Eleanor and Robyn that he'd tried to show the Stranger. His first sword, notched and weathered but sharp and unrusted, as it had been when he first laid hands on it. Robyn's sketchbook. Lou's favorite hatpin. His first pocketwatch, painstakingly handwound for decades, long ago shattered irreparably to pieces - )
It takes him several minutes just to gather himself enough to reach out, and even then he is trembling fairly badly.
(Is this real? Has any of this been real? He's been shot in the head before and his brain kept working just fine, he's only ever hallucinated when on a staggering quantity of drugs and he doesn't remember taking any, but maybe it is a dream, or a trick, or...)
The water in the well is not real. His hand passes through it without resistance, like a mirage.
But his hand closes on a real object, and when he pulls it back out, heart in his throat, it does not disappear.
Hob Gadling has had hundreds of years to get used to losing things, see. By the time he was married, by the time he had a child, he was used to objects being fundamentally perishable. He still gets attached - he can't not, no matter how hard he tries - but anything he's ever laid hands on since maybe the third or fourth time he died, at best, has been with the quiet understanding, in the back of his mind, that it's eventually going to be gone. There is no such thing as careful enough. You can have a thing or you can preserve it, never both.
But when he was young, he didn't know.
When he was young, he thought to himself, people die but things don't, if only I am very careful I can keep them. And so he'd saved his pennies, slowly, painstakingly, for decades, dreaming of seeing past the reach of an illiterate peasant soldier, dreaming of finding new things about the world to love that he could not have imagined as a child, and he had bought a book. So he could learn to read.
The Canterbury Tales, hand-scribed and illuminated. He'd read it so many times he could probably still recite it. He had been so, so careful, with this most beloved of objects, imagining it possible to keep, this first key he had found to the world outside his immediate field of view. Wrapped it carefully in oilcloth, never bent the pages, re-bound it by hand with fresh twine a half-dozen times.
It had been dust in his hands by 1500.
"Oh," he says, very softly, as he sits, fingertips brushing over the achingly familiar texture of old linen paper. "Oh, thank you so much."
(He's not really going to get to keep it. It will dissolve again, eventually. He'll love it all the more, until then, knowing.)