ADVANCE OF ASTRONOMY. 299 



on this earth. But this is not the case. Indeed, at the present 

 moment it seems doubtful if there be any element which spectrum 

 analysis has hitherto disclosed in the celestial bodies which is not 

 also a recognized terrestrial body. The well-known case of helium 

 gives a striking illustration. In the year 1868 Sir jSTorman Lockyer 

 detected the presence of rays in the solar spectrum which were 

 unknown at that time in terrestrial chemistry. These rays ap- 

 peared to emanate from some substance which, though present in 

 the sun, did not then appear to belong to the earth. This element 

 was accordingly named " helium," to indicate its solar origin. 

 Twenty-five years later Professor Kamsay discovered a substance 

 on the earth which had been hitherto unrecognized, and which, on 

 examination, yielded in the spectrum precisely those same rays 

 which had been found in the so-called helium from the sun. In 

 consequence of this discovery this element is now recognized as a 

 terrestrial body. It is indeed a remarkable illustration of the 

 extraordinary character of modern methods of research that a sub- 

 stance should have first been discovered at a distance of nearly one 

 hundred million miles, that same substance being all the time, 

 though no doubt in very small quantities, a constituent of our 

 earth as well as of the sun. 



Much has been done within the past century in many other 

 branches of astronomy. I must especially mention the important 

 subject of meteoric showers. For the development of our knowl- 

 edge of this attractive part of astronomy we are largely indebted 

 to the labors of the late Prof. H. Newton, of Yale. By his inves- 

 tigations, in conjunction with those of the late Professor Adams, 

 it was demonstrated that the shower of shooting stars which usually 

 appears in the middle of ITovember is derived from a shoal of small 

 bodies which revolve around the sun in an elliptic track, and accom- 

 plish that circuit in about thirty-three years and a quarter. The 

 earth crosses the track of these meteors in the middle of November. 

 If it should happen that the great shoal is passing through the 

 junction at the time the earth also arrives there, then the earth 

 rushes through the shoal of little bodies. These plunge into our 

 atmosphere, they are ignited by the friction, and a great shower is 

 observed. It is thus that we account for the recurrence of spe- 

 cially superb displays at intervals of about thirty-three years. 



But one more great astronomical discovery of this century 

 must be mentioned, and here again, as in so many other instances, 

 we are indebted to American astronomers. It was in 1877 that 

 Prof. Asaph Hall discovered that the planet Mars was attended 

 by two satellites. This was indeed a great achievement, and 

 excited the liveliest interest and attention. Since the days when 



