P.

Penjal traps, 135.

Pepys and skating, 273.

Perry, coefficient of friction of greased surfaces, 265.

Phobos, dimensions of, 177; orbit of, 177.

Photoelectric activity and absorption, 207; persists at low temperatures, 208, 209; not affected by solution, 213.

Photo-electric experiment, 205; sensitiveness of the hands, 207; theory of latent image, 204, 209 et seq.

Photographic reversal, experiments on, by Wood, 211; theory of, 210.

Piazzi, discovery of first Asteroid, 175.

Pickering, W. H., observations on Mars, 167.

Planet, slowing of axial rotation of, 189.

Plant, expectant attitude of, 109.

Pleochroic haloes, measurements of, 224; theory of, 224 et seq.; true form of, 226; radius of, and the additive law, 225; absence of actinium haloes, 225; see also Haloes; mode of occurrence of, 223 et seq.

Poole, J. H. J., proportionality of thorium and uranium, 26.

Poulton, uniformity of past climate, 17.

Pratt, Archdeacon, and isostasy, 53.

Prealpes, exotic nature of, 150, 151.

Prematerial universe, nature of a, 297, 300.

Prestwich and thickness of rigid crust, 128; history of the
Pyrenees, 140.

Primitive organisms, interference of, 89; life-curves of, 88.

Proctor and orbits of Asteroids, 176.

Protoplasm, encystment of, 68.

Purana Era of India, 134.

Pyrenees, history of, 140.

R.

Radioactive elements concerned in mountain building, 125.

Radioactive layer, failure to account for deep-seated temperatures, 127; assumed thickness of, 128; temperature at base of, due to radioactivity, 129; in the upper crust of the Earth, 125; thickness of, 126-128.

Radioactive treatment, physical basis of, 251.

Radioactivity and heat emission from average igneous rock, 126; rarity of, established by haloes, 241, 243.

Radium, chemical nature and transmutation of, 244-245; emanation of, 245; rays from, 253, 254; table of family of, 253; period of, 253; small therapeutic value of, 254.

Radium C, therapeutic value of, 254; rays from. 254; generation of, 254.

Rationality, conditions for development of, 163.

Rays, similarity in nature of gamma, X, and light rays, 248; effects on living cell, 251; penetration of, 251.

Reade, T. Mellard, finding age of ocean by calcium sulphate, 13.

Recumbent folds, formation of, 155 et seq.

Regelation, 284; affecting glacier motion, 285.

Reversal, photographic, explanation of, 211.

Richards and Lembert, atomic weight of lead, 27.

Richter, Jean Paul, Dream of the Universe, 200.

Rock salt in the ocean, amount of, 13.

Rocks, average composition of, 43; radioactive heat from, 126; rate of solution of, 36.