x ments can be determined (for example, ref. 20). Even- tually, it is anticipated that the logistically difficult im situ approach will be completely superseded by direct measure- ments of radiation incident on representative individuals in their daily rounds. We thank our colleague, H. L. Beck, as well as several Health and Safety Laboratory summer students, including J. Grebowsky, H. Grotch and I. Hammerman, for their assistance with the outdoor survey. A. Spiegal carriod out the indoor measurements. Many helpful discussions have been held with Dr. A. Segall of the Harvard School of Public Health, who co-ordinated the various parts of the New England survey and who kindly supplied the dosimeter results. We also thank J. E. McLaughlin, director, Radiation Physics Division, Health and Safety Laboratory, for his advice and support. . oy . : an 1 Segall, A., Science, 140, 1337 (1963). * Lowder, W. M., Segall, A., and Condon, W. J., in The Natural Radiation Environment, edit. by Adams, J. A, S., and Lowder, W. M. (Univ. Chicago Press, 1964). * Segall, A., and Reed, R., Arch. Env. Health, 9, 494 (1964). ‘Condon, W. J., Lowder, W. M., and Beck, H. L., Health and Safety Lao. _ i Rep. (to be published, 1965). . te : , wy Billings, M. P., Harvard Univ. (unpublished results). * Spiers, F. W., App. D, in The Hazards to Man of Nuclear and Allied Radiations; A Second Report to the Medical Research Council (H.M. Stationery Office, London, £966), “Et Spiers, F. W., McHugh, M. J.,and Appleby, D. B., in The Natural Radiation j ‘Halm, E., Herbst, W., and Mastrocola, A., Sonderdr. aus Beilage B., No. 6/1962, zum Bull. des Eidg. Gesundhetisamtes (Dec. 22, 1962). "Spiers, F. W., and Overton, T. R., Phys. Med. Biol., 7, 35 (1962). 0 O’Brien, K., Lowder, W. M., and Solon, L. R., Rad. Res., 9, 216 (1858). “ Lowder, W. M., Beck, H. L., and Condon, W. J,, in The Natural Radiation Environment, edit. by Adams, J. A. §., and Lowder, W. M. (Univ. Chicago Press, 1964). “Lowder, W. M., Beck, H. L., and Condon, W. J., Nature, 202. 745 (1964). 18 Beck, H. L., Condon, W. J., and Lowder, W. M., Health and Safety Laboratory Report HASL-150 (1964), me Environment, edit. by Adams, J, A. 8., and Lowder, W. M. (Univ. Chicago Press, 1964). “ Beck, H. L. (to be published, 1965). 1 18 7 18 Lowder, W. M., Beck, H. L., and Condon, W. J. (to be published, 1965). Roesch, W. C., MeCall, BR. C., and Rising, F. L., Health Phys.,1, 340 (1958). Segall, A., Shapiro, J., and Worcester, F. (to be published). Rep. U.N. Sei. Camm. Effects of Atomic Radiation (United Nations, New York, 1962, App. £). uw Oe eEe} K., Soton, L. BR., and Lowder, W. M., Rev. Set. Instr., 29, 1097 a *0 Roser, F. X., and Cullen, T. L., Sctence, 138, 145 (1962). 21 Henson, P. W., Phys. Med. Biol., $, 423 (1963). “McLaughlin, W. L., J. Photogr. Sci. (to be published, 1965). 28 McCall, R. C., and Fix, R. C., Health Pays., 10, 602 (1964). * Blase, E, F., Logerquist, R, F., Paimer, R. C., and Rutland, D, I, Health Phys, 9, 888 (1963). * Cullen, T. LE. (personal communication, 1964). Printed in Great Britain by Fisher, Knight & Co., Ltd., St. Albans,