Data pulled from Appendix 5 in "Graphical Methods for Data Analysis", Chambers, Cleveland, Kleiner and Tukey. 

Rainfall in acre-feet from 52 clouds, of which 26 were chosen randomly and seeded with silver oxide. 

Source:
Simpson, J., Olsen, A., and Eden, J. C. (1975). A Bayesian analysis of a
multiplicative treatment effect in weather modification.
Technometrics 17, 161-166. [Chapters 3, 6]