2 14 THE POPULAR SCIENCE MONTHLY 



7. The Mount Hamilton and Santiagoz spectograpMc observations of stel- 

 lar motions have shown that stars effectively young are traveling slowly, middle- 

 aged stars more rapidly, and old stars more rapidly still; that is, that the 

 velocities of the stars increase with their effective ages. 



8. Observations have established that those nebulae known as planetary 

 nebulae are traveling through space with average speeds even higher than the 

 average speeds of the stars. It had previously been supposed that these nebulse 

 represented a stage of existence antecedent to the stellar age. The high veloci- 

 ties of these objects have created the opinion that they have more probably been 

 formed from stars which have been overtaken by catastrophes, such as collisions 

 with other celestial objects. 



9. The North Pole Star was found to be a triple star, in 1899, by means of 

 spectrographic observations. The first magnitude star Capella was discovered to 

 consist of two stars revolving around their center of mass in 104.1 days, the two 

 nearly equal components being inseparable in our largest telescopes. 



10. In the same manner about 250 spectroscopic binary stars have been 

 found at Mount Hamilton and Santiago. 



11. A study of the orbits of spectroscopic binary stars has established that 

 the component stars in a system whose spectrum indicates early age are rela- 

 tively very close together, requiring very short periods of revolution, and that 

 the orbits are nearly circular. In systems whose spectra show them to be of 

 greater effective ages, the distances separating the components are successively 

 greater, on the average, and their orbits are more eccentric. The observed 

 facts on the subject are fully confirmative of existing mathematical theories of 

 the evolution of double star systems. 



12. The Crossley reflecting telescope established for the first time the tre- 

 mendous advantage of this form of telescope in the photography of certain 

 classes of celestial objects, such as nebulte, star clusters, etc. 



13. Before the Crossley reflector was in use about 10,000 nebulae had been ' 

 discovered at various observatories. A few dozens of these were known to be 

 spiral in form. The Crossley photographs led to the discovery of many hun- 

 dreds of additional nebulee in the extremely small part of the sky covered by 

 the photographs. It was a simple matter to calculate that certainly 120,000 and 

 possibly half a million nebulte await discovery whenever time can be spared for 

 the Crossley reflector to undertake this work. These photographs led to the 

 iiniexpeeted discovery that a majority of the nebuloe are of spiral form — un- 

 doubted evidence of their rotation. 



14. The extensive series of photographs of the minor planet Eros and sur- 

 rounding stars, with the Crossley reflector, led to a new and accurate determina- 

 tion of the distance from the earth to the sun. 



15. Eight total solar eclipses have been successfully observed by expeditions 

 whose expenses were defrayed by friends of the observatory. 



16. It has been shown that the new stars appearing in recent years have 

 been converted into nebulae, and later, in many cases, into extremely faint stars 

 of apparently normal condition. 



17. Many thousands of extremely accurate positions of the stars have been 

 secured with the meridian circle. 



18. Very extensive observations of double stars, comets, planets, and satel- 

 lites have been made. 



19. A large number of orbits have been computed for visual double stars, 

 spectroscopic binary stars, comets, and asteroids. 



20. Extensive additions have been made to our knowledge of the spectra of 

 nebulae, comets, new stars, and stars of special interest. 



2 Santiago, Chile, is the location of the D. O. Mills Observatory, which is 

 administered by the director of the Lick Observatory, 



