ANNALS OF THE ACADEMY 83 



present case, this labor has been greatly simplified by the recent publication by Sir 

 William and Lady Huggins, of an Atlas of Representative Spectra from wave 

 length 4,870 to 3,300, together with a discussion of the evolutional order of the 

 stars, and the interpretation of their spectra, preceded by a short history of the 

 Observatory and its work. This monumental volume not only furnishes a state- 

 ment of the various publications of the authors, but exhibits the relation of the 

 various investigations undertaken much better than could readily be done by 

 another. From this it appears that the work began in 1856 with a 5-inch DoUand 

 equatorial, which was replaced two years later by an excellent 8-inch Clark tele- 

 scope. In 1870 this was again replaced by a 15-inch achromatic and an 18-inch 

 reflector. In 1858 Sir William, then Mr. Huggins, undertook with Dr. Miller 

 the visual study of stellar spectra. This work was continued until 1864, and the 

 results were communicated to the Royal Society. Soon after this, on August 29, 

 1864, Sir William made one of the great discoveries in astrophysics. He found 

 that the spectrum of the planetary nebula in Draco, N. G. C. 6543, had a mono- 

 chromatic spectrum. 



" It has heretofore been supposed that all nebulfe might consist of distant stars 

 and could be resolved into their components by a telescope of sufficient power. 

 This theory was at once disposed of, and it appeared that of 60 of the brighter 

 nebulae and clusters about one-third were of this gaseous character. In 1866 

 the observations of the new star in Corona gave the first clew to the cause of 

 these remarkable objects. In 1868 Sir William was able to announce the first 

 step in an investigation which in recent years has become one of the most impor- 

 tant in astrophysics. The hydrogen lines in the brightest stars showed a slight 

 displacement, from which the motion of these bodies In the line of sight may be 

 determined. The accurate measurement of this quantity is now occupying a 

 large part of the time of the greatest telescopes in the world. It Is leading to 

 unexpected results, which throw important light on the formation of the universe. 

 The fact that these displacements are wholly independent of the distance of the 

 source of light gives an opportunity to study problems for which ordinary visual 

 methods fail entirely. About this time, also, a study of comets showed that their 

 spectra closely resembled that of defiant gas. A proposal of great scientific 

 importance was a method of observing the solar protuberances In the uneclipsed 

 sun. This method was devised independently by Mr. Lockyer. It Is now 

 claimed that these remarkable phenomena can be better seen any clear day at a 

 fixed observatory than with portable instruments during a total solar eclipse. In 

 1876 the study of the spectra of the stars by means of photography, which had 

 been attempted without attaining satisfactory results in 1863, "'as undertaken. 

 Among the results published four years later, one of the most important was the 

 discovery of the wonderful series of lines due to hydrogen. Similar series of lines 

 are now found to exist In the spectra of many other terrestrial elements, and form 

 the basis of the spectroscopic relation of these substances with one another. 



