The Spring-Rocked Cradle: Tapered Springs and a Treadle

"The nature of this invention relates to improvements in cradles; and the invention consists in mounting the cradle or crib upon a suitable frame in such manner that it may be rocked by a treadle, one end of which impinges against said spring, and by which the impulse necessary to rock the cradle may be given". "The springs G are common flat bars, tapering from their upper ends downward". "The manner of rocking the crib upon the lower frame will be plainly seen, the springs G tending to resist too rapid movement as the center of gravity of the crib is carried over to either side, their tapered forms distributing the strain upon them, which is naturally heaviest at their upper ends, so as to make their flexure equal at any part of their lengths". "This improvement may be readily adapted to rocking-chairs, &c."

Make a small box (the crib) and pivot it on a dowel through its ends, a little below its middle, resting on two plywood uprights. Fix a strip of spring steel upright at each end so that the crib's rocking bends it. Load the crib with a weight, tip it and let go. Time ten swings with the stopwatch. Add weight higher up in the box and time it again: it slows, and with enough weight high up it tips over. Swap in a stiffer strip and repeat. Compare with the notebook.

**Dwight M. Cobb** of Galesburg, Illinois, filed US 157,269 on 9 June 1874; it is dated 1 December 1874. A catch holds the crib still when rocking is not wanted. **Honest limits.** The notebook treats rocking as small swings with linear springs and ignores friction; the tapered-spring figures assume a simple cantilever of constant thickness. All values are examples. Your timed swings are the measurement.