REFERENCES AND NOTES Solon, L.R., Lowder, W.M., Shambon, A., and Blatz, H., "Investigations of Natural Environmental Radiation", Science 131, No. 3404, 903 (March 25, 1960). Shambon, A., Lowder, W.M., and Condon, W.J., "Ionization Chambers for Environmental Radiation Measurements", Health and Safety Laboratory Report, HASL-108 (February 1963). A detailed report on our spectrometric methods as well as separate reports on our cosmic ray dose rate investigations and surveys in New England and New York State will be published in the near future. References 4 and 5 contain more detailed summaries of our calibration and spectral analysis procedures, Lowder, W.M., Condon, W.J., and Beck, H.L., "Field Spec- trometric Investigations of Environmental Radiation in the U.S.A." Ch. 35 in The Natural Radiation Environment, J.A.S. Adams and W.M. Lowder, eds. (Univ. of Chicago Press, Chicago, 1964). Lowder, W.M. Beck, H.L. and Condon, W.J., "The Spectrometric Determination of Dose Rates from Natural and Fallout Gamma Radiation in the United States, 1962-1963", Nature (in press). Appendix in The Natural Radiation Environment, J.A.S, Adams and W.M. Lowder, eds. (Univ. of Chicago Press, Chicago, 1964). Lowder, W.M., Segall, A., and Condon, W.J., "Environmental Radiation Survey in Northern New England", Ch. 56 in The Natural Radiation Environment, J.A.S. Adams and W.M. Lowder, eds. (Univ. of Chicago Press, Chicago, 1964). Foote, Robert: S., "Time Variation of Terrestrial Gamma Radiation", The Natural Radiation Environment, J.A.S. Adams and W.M. Lowder, eds. (Univ. of Chicago Press, Chicago, 1964). Guillou, Robert B., "The Aerial Radiological Measuring -12 -