But before I was to experiment with live volcanoes came a decade of laboratory experiment.
Chapter II
Imitating Ripplemarks
“The Constitution is an experiment, as all life is an experiment.”
At the end of the century my experiments with the sclerometer, and with the class in experimental geology, steered me for years into laboratory experiment. Europe was headed toward geophysics and geochemistry, meaning chiefly mathematical and statistical analysis. My vision was nonmathematical, though I used pressures, temperatures, clocks, and yardsticks to measure erosion, sediment, warping of strata, and melting.
This took me away from petrography, for the polarizing microscope was dealing with infinite series of minerals and molecules. I could see nothing but infinite penetration into the smaller and smaller. Clarence King and Frank Perret had been on the way to infinite journeying outward to the bigger and bigger.
The guiding formula was “erosion, sedimentation, deformation, and eruption.” Measure these on the globe, imitate them with mud pies in the laboratory. Compare the global examples with the mud pies. Try to get the mud pies to illuminate the gigantic stream systems, flood plains, sea bottoms, folded mountains, intrusions, and lavas of the earth. Then try to measure in the field those processes with observatories. So, to me, came the transition from collections to experiments.
The machinery of nature, whether with sand heaps or sand grains or coral pebbles, is the same. It is impelled by currents flowing over loose materials which make eddies in the lee of lumps. The eddies are either billows or cyclones. At the middle they are billows; at the ends they are cyclones. The billow eddies obstruct the heaping. The cyclone eddies lengthen the heaps right and left of the current direction. George Darwin studied the eddies by means of a drop of thick ink in a glass tank on top of a ripple ridgelet. The ink migrated to form underwater billows and cyclones, or vortexes. He used a dropper to place the ink globule, and then watched the vortexes form as he oscillated the tank.
Low parts travel fastest, namely the points. High parts build on the upstream side, and travel slowest, and the stuff tumbles over the crest line and is corniced by the eddy. Snow does it, pebbles under sea do it, and marine life adapts itself to it, wherever the food supply is best.
In the study of ripplemarks, Harry Gummeré, a graduate in astronomy, was my collaborator. Ripplemarks are made by back-and-forth eddies on the bottom, while big waves oscillate the water. We moved the bottom instead of making waves in the water. A glass plate sprinkled with sand under water in a tank was oscillated back and forth horizontally. It was clamped under a carriage which oscillated on wire tracks stretched across the tank. A string pulled the carriage against an elastic on the other side. A wooden wheel and crank, set upright edgeways, had holes and pegs to pull on the string, and the crank turns were timed with a metronome. The holes in the flat wheel were a centimeter apart, so that a revolution of the wheel pulled the string for every two centimeters of travel of the carriage. Thus the sand-covered plate was jerked back and forth under water two centimeters, four centimeters, six centimeters, and so forth; once a second, or two seconds, or three seconds, and so forth, by beats of the metronome.
The result was beautiful ripplemarks on a glass which could be lifted out of the water, dried, and placed over blueprint paper to preserve the record. The sizes of ridge to ridge ripples were from a fraction of an inch to two or more inches. The little ones diminished to zero when the jerking was small, the big ones washed out when the jerking was too big.