VI CONTENTS. 



GENERAL APPENDIX. _. 



Page. 



1. The Discovery of Helium, and What Came of It, by C. G. Abbot 121 



2. An Account of the Rise of Navigation, by R. H. Curtiss 127 



3. The Tornadoes of the United States, by Prof. Robert DeC. Ward 13'.) 



4. Wind Power, by James Carlill 147 



5. A Tribute. Samuel Pierpont Langley : Pioneer in Practical Aviation, 



by Henry Leffman 157 



6. Twentieth Century Physics, by R. A. Millikan 169 



7. The Experiments of Dr. P. W. Bridgman on the Properties of Mat- 



ter When Under High Pressure. Introductory Note by C. G. 



Abbot 185 



S. The Problem of Radioactive Lead, by Theodore W. Richards 205 



9. Sphagnum Moss: War Substitute for Cotton in Absorbent Dress- 

 ings, by Prof. George E. Nichols . 221 



10. History of Military Medicine and its Contributions to Science, by 



Col. W. P. Chamberlain 235 



11. Some problems of International Readjustment of Mineral Supplies as 



Indicated in Recent Foreign Literature, by Eleanora F. Bliss 251 



12. Reptile Reconstructions in the United States National Museum, by 



Charles W. Gilmore 271 



13. A Pleistocene Cave Deposit in Western Maryland, by J. W. Gidley 2S1 



14. Paleobotany : A Sketch of the Origin and Evolution of Floras, by 



Edward W. Berry 289 



15. The Direct Action of Environment and Evolution, by Prince Kropotkiu_ 409 



1G. The Law of Irreversible Evolution, by Branislav Petronievics 429 



17. The Fundamental Factor of Insect Evolution, by S. S. Chetverikov 441 



IS. The Psychic Life of Insects, by E. L. Bouvier 451 



19. Sexual Selection and Bird Song, by Chauncey J. Hawkins 461 



20. Marine Camoufleurs and Their Camouflage : The Present and Pros- 



pective Significance of Facts Regarding the Coloration of Tropical 



Fishes, by W. H. Longley 475 



21. Foot-Plow Agriculture in Peru, by O. F. Cook 487 



22. Sun Worship of the Hopi Indians, by J. Walter Fewkes 493 



23. A Constitutional League of Peace in the Stone Age of America : The 



League of the Iroquois and Its Constitution, by J. N. B. Hewitt 527 



24. The Problem of Degeneracy, by H. F. Tredgold 547 



25. History in Tools, by W. M. Flinders Petrie 563 



26. The Background of Totemism, by E. Washburn Hopkins 573 



27. A Great Naturalist : Sir Joseph Hooker, by Sir E. Ray Lankester 585 



