Canals and "canali," 166; curvature of, and path of a satellite, 188 _et seq._; double and triple accounted for, 186, 187; doubling of, 195; disappearance and reappearance of, 196-198; photography of, 198; not due to cracks, 167; not due to rivers, 167; of Mars, double nature of, 166, 170; crossing dark regions of planet's surface, 168; of Mars, Lowell's views on, 168 _et seq._; shown on Lowell's map, investigation of, 192 _et seq._; radiating, explanation of, 193, 194; number of, 194; developed by secondary disturbances, 194; nodal development of, due to raised surface features, 195. Chamberlin and Salisbury, the Laramide range, 121. Clarke, F. W., estimate of mass of sediments, 9; age of Earth by sodium collection, 14; average composition of sedimentary and igneous rocks, 42; on average composition of the crust, 126; solvent denudation of the continents, 17, 40. Claus, protoplasm the test of the cell, 67; abortion of useless organs, 69. Coefficient of friction, definition of, 262; deduction of, from angle of friction, 263; abnormal values on ice, 261-265, 282; for various substances, 265. Continental areas, movements of, 144. Cornil and Babes, size of spores, 98. Croll, James, dawn of evolution, 301. Crust of the Earth, average composition of, 126; depth of softening in, 128. Curie, definition of the, 256. D. Dana, on mountain building, 120. Dawson, reduction of surface represented by Laramide range, 123. Deccan traps, 137 _deferlement_, theory of, 155; explanation of, 155 _et seq._; temperature involved in, 156. Deimos, dimensions of, 177; orbit of, 577. De Lapparent, exotic nature of the Prealpes, 150. De Montessus and the association of earthquakes with geosynclines, 142. Denudation as affected by continental elevation, 17; factors promoting, 30 _et seg._; relative activity in mountains and on plains, 35-40; solvent, by the sea, 40; the sodium index of, 46-50; thickness of rock-layer removed from the land, 51. De Quincy, System of the Heavens, 200. Dewar, Sir James, latent image formed at low temperatures, 202. Dixon, H. H., and AGnadance of Life, 60. Double canals, formation by attraction of a satellite, 585-187. Douglass, A. E., observations on Mars, 167. Dravidian Era of India, 135. E. Earth, early history of, 3, 4; dimensions of, relative to surface features, 117. Earth's age determined by thickness of sediments, 5; determined by mass of the sediments, 7; determined by sodium in the ocean, 12; determined by radioactive transformations, 19; significance of, 2. Earthquakes associated with geosynclincs, 142. Efficiency, tendency to maximum, in organisms, 113, 114. Elements, probable wide diffusion of rare, 230; rarity of radioactive, 241. Elster and Geitel, photo-electric activity and absorption, 207; photo-electric properties of gelatin, 212; Emanation of radium, therapeutic use of, 256-259; advantages of, in medicine, 256; volume of, 257; how obtained, 257; use of, in needles, 258.