Harry Thomason's heat storage scheme.
Hot water from a trickle-down solar water heater is stored in a steel
tank buried in a bin of stones. The stones serve to increase the heat transfer
area of the tank when heating cool air blown through the stones. From William
A. Shurcliff, "New inventions in low-cost solar heating--100 daring schemes
tried and untried", p. 184, Brick House Publishing Company, Andover, Mass.