THE PROGRESS OF SCIENCE FROM 1836 TO 1886. 515 



sis ; while the increasingly important study of meteors and comets has 

 brought us close to the very threshold of the great ultimate mystery 

 of star-genesis and world-forming. The extreme tenuity of the mass 

 of comets, the inconceivable rarity of the matter composing their 

 gaseous tails, the carious phenomena of the instantaneous reversal on 

 passing their perihelion, the proof that their light is partly reflected 

 and partly direct, the spectroscopic determination of their composition, 

 the discovery of the essentially planetary nature of meteor-streams, 

 and the recognition of their vast numbers swarming through space, 

 are among the most striking novelties of the last half-century in this 

 direction. 



In sidereal astronomy, besides the mere mechanical increase of 

 mapping, the chief advances have been made in observations upon 

 double stars, spectroscopic analysis of fixed stars and of nebulae, and 

 consequent proof of the fact that truly irresolvable nebulae do really 

 exist, the gaseous raw material of future stars and solar systems. It 

 must be added that within the half -century the hypothetical ether has 

 amply vindicated its novel claim to take its place as a mysterious entity 

 side by side with matter and energy among the ultimate components 

 of the objective universe. 



In geology, the chief theoretical advances have been made by the 

 recognition of the cosmical aspects of the earth's history ; its relations 

 to nebula, sun, and meteor ; the importance of eccentricity and pre- 

 cession of the equinoxes, and the possible results of ancient changes 

 in its rates of motion, tides, and so forth. Dynamical geology has 

 made vast strides, especially in the investigation of volcanic phenom- 

 ena, mountain-building, and the birth and growth of islands and con- 

 tinents. The science of earth- sculpture has been developed from the 

 very beginning. Stratigraphical geology has been largely improved. 

 And in paleontology an immense number of the most striking and in- 

 teresting of fossil forms have been brought to light. Among them may 

 be specially mentioned those which have proved of critical importance 

 as evidences of the truth of organic evolution the toothed birds of the 

 Western American cretaceous deposits, the lizard-like bird or bird- 

 like feathered lizard of the Solenhofen slates, Marsh's remarkable series 

 of ancestral horses, Cope's beautiful reconstruction of the fossil pro- 

 genitors of existing camels. Monkeys certainly, anthropoid apes 

 clearly, man doubtfully, have been detected in the fossil state. India, 

 Australia, Canada, the United States have been explored and surveyed, 

 geologically and paleontologically ; and the exploitation of the far 

 West in particular has not only added immensely to our knowledge of 

 life in past times, but has also revolutionized our conceptions as to the 

 gradual growth and development of continental areas, and the occa- 

 sional vast scale of volcanic phenomena. The permanence of all great 

 continents and oceans is now a proved truth of geology. It has been 

 re-enforced and extended from a totally different point of view by Al- 



