Was at Walden Pond today with Caroline, who found this model of a lake with ropes representing various depths. I thought it was a clever tactile. Also a great birding by ear session with Jerry Nadier.

Caroline is standing next to a wooden table which has a lake depicted on it. At different points in the lake, there are knobs you can pull up, and ropes that represent the depth. Some are very short. The one she is pulling is at the center of the lake, so it is longer. These represent a method Henry David Thoreau used to measure the bottom of the lake. He wiated until it was frozen solid, and then drilled into the ice and tied a stone to a rope, and left it sink to the bottom. He knew then that the depth of the lake was however far it took for the tension to slacken and the stone to reach the bottom of the lake.