' 94 



of physical instruments and processes, ha ve revolutionized the observa- 

 tory. From a simple observing station, it has been transformed into a 

 great physical laboratory, where images of the Sun and Stars are stu- 

 died with many powerful instruments, and celestial phenom^na are expe- 

 rimentally imitated with the aid of electric furnaces and other sources 

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

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

 the work 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 haif-tone plates, made from the best astronomical neg- 

 atives, show the most recent resultis 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 vsdth Camera Lenses. Developmeat of the Re- 

 flecting Telescope. Elementary Principies of Spectrum Analysis. Gratiug 

 Spectroscopes and the Chemical Composition of the Sun. Phenomena of 

 Sun's Surface. 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 

 Spectroheliograph Plates. A Study of Sun Spots. Stellar Temperatures. 

 The Nebular Hypothesis. Stellar Development. The Meteoritic and Plane- 

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

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

 portunities for Amateur Observers. 



Les récents progres du Systeme Métrique. Eapport présente 

 á la quatriéme Confórence Genérale des Poids et Mesures, reu- 

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

 teur-adjoint du Burean International des Poids et Mesures. 

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

 Villars, Quai des Grands-Augustins, 55. 



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

 oft'rait, á la suite des grands progrés réalisés par le Systeme métrique dans 

 ees derniéres années, une occasion toute natureile d'en faire un exposé 



