All looked well above, but a baby would not be safe standing thereon.

Belton contrived a kind of prop with a weight attached.

This prop would serve to keep the cut section from breaking through.

The attached weight was at rest in a hole left in the wall of the cavity near its top.

If you dislocated the weight, the momentum that it would gather in the fall would pull down the prop to which it was attached.
Finally, Belton fastened a strong rope to the weight, and ran the rope under the schoolhouse floor until it was immediately beneath his seat.
With an auger he made a hole in the floor and brought the end through.
He managed to keep this bit of rope concealed, while at the same time he had perfect command of his trap door.
For two or three nights previous to commencement day Belton had worked until nearly morning filling this cistern with water.