94 



of physical instruments and processes, have revolutionized the observa- 

 tory. From a simple obsei'ving station, it has been transformed into a 

 great physical laboi'atory, where images of tlie Sun and Stars are stu- 

 died with many powerful instruments, and celestial phenompna are expe- 

 rimentally imitated with the aid of electric furnaces and other sources 

 of intense heat. The result has been a great gain ia our knowledge of the 

 origin, development, and decay of stars, This book gives an account of 

 the wovk of the last few years in the Yerkes and Mount Wilson Observa- 

 tories, and thus initiates the reader into the whole study of the stupend- 

 ous problem. 104 half-tone piafes, made fiom the best astronomical neg- 

 atives, show the most reoent result.3 of celestial photography in most of 

 its phases. Professor Hale has shown a most unusual skill in the adapting 

 of difficult material to the comprehension of those who are not specialists 

 in the subject. 



CONTENTS.— The Problem of Stellar Evollution. The Student of the 

 New Astronomy. The Sun as a Typical Star. Large and Small Telescopes. 

 Astronomical Photography with Camera Lenses. Development of the Re- 

 flecting Telescope. Elementary Principies of Spectrum Analysis. Grrating 

 Spectroscopes and the Chemicai Composition of the Sun. Phenomena of 

 Sun's tíurface. The Sun's Surroundings. The Spectroheliograph. The 

 Yerkes Observatory. Astronomical Advantages of High Altitudes. The 

 Mount Wilson Solar Observatory. The Snow Telescope. Some Uses of 

 Speetroheliogi'aph Plates. A Study of Sun Spots. Stellar Temperatures. 

 The Nebular Hypothesis. Stellar Development. The Meteoi-itic and Plane- 

 tesimal Hypotheses. • Does the Solar Heat Vary? The Construction of 

 Large Reflectiug Telescopes. Some Possibilities of New Instruments. Op- 

 portunities for Amateur Observers. 



Les récents progres du Systeme Métrique. Rapport presenté 



álaquatriémeConférenoe Genérale des Poids et Mesures, reu- 

 nió á Paris en Octobre 1907, par Ch.-Ed. Guillaume, Diree- 

 teur-adjoint du Bureau international des Poids et Mesures. 

 In-4, 94 pages, 4 figures; 1907. 5 fr. — Paris. Librairie Gauthier- 

 Villars, Qaai des Grands-Augustins, 55. 



La reunión de la quatriéme Conf érence genérale des Poids et Mesures 

 ofErait, á la suite des grands progrés réalisés par le Systeme métrique dans 

 ees derniéres anaées, une occasion toute naturelle d'en faire un exposé 



