What is the name/author/publication of a science fiction, very short story, about an autistic child who is observed to create an anti-gravity machine from junk in his back yard, then dismantles it.
What is the name/author/publication of a science fiction, very short story,
"The Available Data on the Worp Reaction", a short short story (less than 4 pages) by Lion Miller; also the (unaccepted) answer to the old question Short story from 60's or before about building infinite energy source from rubbish pile. It was first published in The Magazine of Fantasy and Science Fiction, September 1953, available at the Internet Archive. An audio of somebody reading the story is available on YouTube.
about an autistic child
The main character has some sort of mental condition, not identified as autism in the story:
The earliest confirmed data on Aldous Worp, infant, indicates that, while apparently normal in most physical respects, he was definitely considered by neighbors, playmates, and family as a hopeless idiot. We know, too, that he has a quiet child, of extremely sedentary habits. The only sound he was ever heard to utter was a shrill monosyllable, closely akin to the expression "Whee!" and this only when summoned to meals or, less often, when his enigmatic interest was aroused by an external stimulus, such as an odd-shaped pebble, a stick, or one of his own knuckles.
Moreover, he was not a child but a young man when he completed his anti-gravity device:
Thus began a project that did not end for nearly twenty years. Young Worp progressed through childhood, boyhood, and young manhood, transferring thousands of metal objects, large and small, of nearly every description, from the dump to the coop. Since any sort of formal schooling was apparently beyond his mental capacity, his parents were pleased by the activity that kept Aldous happy and content.
Who is observed to create an anti-gravity machine from junk in his back yard,
We now quote from the combined reports of Major Armstrong and Dr. Cross: "After standing dazed-like for a few minutes, Worp finally came very close to his assembly. There was a rod sticking out with the brass ball of a bedpost fastened to it. Aldous Worp gave this a slight tug. What happened then was utterly fantastic. First, we heard a rushing sound, something like a waterfall. This sound grew appreciably louder and, in about fifteen seconds, we saw a purplish glow emanate from beneath the contraption. Then, the whole congeries of rubbish arose into the air for a height of about three meters and hung there, immobile. The lad Aldous jumped around with every semblance of glee and we distinctly heard him remark 'Whee!' three times. Then he went to one side of the phenomenon, reached down and turned over the rusty wheel of a coffee mill and his 'machine' slowly settled to earth."
then dismantles it.
Systematically, and in order of installation, he removed each part from his structure and carefully returned it to its original place in the original heap by the chicken coop.