IV ANNUAL REPORT SMITHSONIAN INSTITUTION, 1951 



Page 



The mechanics of snakes, by Alfred Leutscher 303 



Hormones and the metamorphosis of insects, by V. B. Wigglesworth 313 



Utilizing our soil resources for greater production, by Robert M. Salter... 319 



The carbon-14 method of age determination, by Frank H. H. Roberts, Jr. 335 

 River Basin Surveys: The first five years of the Inter-Agency Archeological 



and Paleontological Salvage Program, by Frank H. H. Roberts, Jr 351 



Artificial lighting in America: 1830-18G0, by C. Malcolm Watkins 385 



The development of the halftone screen, by Jacob Kainen 409 



The artist and the atom, by Peter Blanc 427 



LIST OF PLATES 



Secretary's report: 



Plates 1, 2 52 



Plates 3, 4 108 



Stormy weather on the sun (W. O. Roberts): Plates 1, 2 174 



Ultrasonics (Laufer): Plates 1-3 222 



Electronics (Zworykin): Plates 1-4 238 



Insides of metals (Zapffe) : Plates 1-4 262 



Enzymes (Kilby) : Plato 1 286 



Fauna of America (Clark) : Plates 1-8 294 



Mechanics of snakes (Leutscher) : Plates 1-3 310 



Hormones and the metamorphosis of insects (Wigglesworth): Plates 1-4. . 318 



Utilizing our soil resources (Salter): Plate 1 334 



River Basin Surveys (F. H. H. Roberts): Plates 1-10 374 



Artificial lighting (Watkins) : Plates 1-8 390 



Halftone screen (Kainen): Plates 1-12 422 



Artist and the atom (Blanc) : Plates 1-5 430 



