 What main motivation did Antler Park have to leave the lens in the barracks?
What with red-spot fever, talking cockatoos and flagpole trees, I was running in circles—especially since Grannie became twins every now and then. We had left the offices of Interstellar Voice three days ago, Earth time, and now as the immense disc of Jupiter flamed across the sky, entered the outer limits of the Baldric. If my calculations are right, we've hit it at its narrowest spot." He could be excused this time, however, for this was only our third day on Jupiter's Eighth Moon, and the country was still strange to us. Blood-and-thunder as these books are, however, they have one redeeming feature—authenticity of background. Grannie Annie was the original research digger-upper, and when she laid the setting of a yarn on a star of the sixth magnitude, only a transportation-velocity of less than light could prevent her from visiting her "stage" in person. As for Xartal, he was a Martian and was slated to do the illustrations for Grannie's new book. And then I was shaking hands with Antlers Park, the manager of I. V. himself. Antlers Park flicked the ash from his cheroot and shrugged. It's no use to the people of Earth but of untold value on Mars. Then it was found that this ore, Acoustix, revitalized their sounding apparatus, and the rush was on." So now here we were at the outer reaches of the Baldric, four travelers on foot with only the barest necessities in the way of equipment and supplies. Xartal, the Martian illustrator, already had a notebook in his hands and was sketching a likeness of the creature. Attached to its hood was a taut wire which slanted up into the sky to connect with the kite. Apparently these adjustments moved planes or fins on the kite and accounted for the car's ability to move in any direction. "They walk out into the Baldric," he continued, "and nothing can stop them. Fully two hundred cockatoos were perched upon it. Silent Xartal, the Martian illustrator, took a chair in a corner and got his notebook out, sketching the room's interior. Failure to produce during a period of thirty days or more, and you lose all rights." "The entire crew of Shaft Four have gone out into the Baldric," he said slowly. A pontocated glass lens, three or four Wellington radite bulbs, each with a spectroscopic filament, a small dynamo that would operate on a kite windlass, and a quantity of wire and other items.
 He knew the value of this spot for Acoustix, and wanted to run the Jimmy Baker out.
 He didn't fully understand the effects of the infra-red rays and wanted to see what it was capable of.  He knew the value of this spot for Acoustix, and wanted to run the Jimmy Baker out.  He was afraid of Grannie Annie discovering his plot and tried to get rid of her.  He had struck a large load of Acoustix and wanted to hide the evidence.