The Tipping-Platform Rat Trap: A Disk That Rights Itself

"The disk I prefer to make of light wood, so that it will tilt very easily when even a slight weight is put upon it." "As rats and mice are very wary and cunning, I contemplate for the first night or two inserting the locking-pins K K, so as to render the disk immovable. After they have got accustomed to coming to the trap for their food, with which it is baited each night, and to playing over the disk or platform, the trap is again set with the locking-pins removed." "As said platform is situated below the points of support from which it is hung, it will, as soon as it has turned up vertically and deposited the rat, turn back again immediately into a horizontal position, ready to entrap the next comer."

Cut a disk from thin plywood about 2 cm smaller than the bucket's mouth, so it can turn inside the rim without touching it. Draw a line across its centre. Screw two screw eyes into its top face on that line, one near each edge. Screw three or four washers to the centre of its underside as the balancing weight. Saw two notches opposite each other in the bucket's rim. Push the dowel through the screw eyes and lay its ends in the notches. Add or remove washers until the disk hangs level and swings back when you tip it. Drill two small holes through the bucket wall just under the disk's edge, opposite each other and at right angles to the dowel. Push a nail through each hole so it props the disk, and tie each nail to the bucket with string. Weigh out a 20 g and a 250 g object on the scale, set each in turn 6 cm from the dowel, and compare the tilt with the notebook. Lean a board against the bucket as a ramp. Put cheese on the disk and leave the nails in for the first nights. When the bait is being taken, pull the nails out. Keep the bucket dry, and check it every morning.

**Seaborn H. B. Harwell** of Morgan County, Georgia, filed US 290,580 on 26 July 1883; it is dated 18 December 1883. His vessel was "nearly filled with water" and the patent says the catch was drowned. It also shows a vessel shaped like a truncated cone, whose inward-sloping sides "would effectually prevent any climbing up and out". This rung builds it dry, to catch the animal alive. **Honest limits.** The notebook treats the disk as rigid and the animal as standing still; a moving animal adds forces the notebook leaves out. Masses, depths and the grip angle are examples. Your weights on the disk are the measurement.