A. Common, I. Roberts, J. N. Lockyer 171 



his range in an unexpected direction. The history of science 

 can furnish no more striking instance of an almost unlimited 

 field of research suddenly opened out by a simple application 

 of a few laboratory experiments. The most successful of the 

 workers who utilized the great opportunities provided by 

 the new method of Spectrum Analysis were Sir Norman 

 Lockyer and Sir William Huggins. Lockyer's first great 

 achievement was the observation in broad daylight of the 

 prominences which up to that time could only be seen during 

 total solar eclipses. He proved that they mainly consisted 

 of glowing hydrogen. The merit of the discovery is in no way 

 diminished by its having almost simultaneously been made 

 by the French astronomer Janssen. Continuing his researches, 

 Lockyer established that the upper layer of the sun's atmo- 

 sphere, which reveals itself at the edge of the solar disc in 

 the form of a bright line spectrum, consisted mainly of the 

 lighter metals such as calcium and barium with hydrogen. 

 A bright yellow line was also universally present which 

 could not be identified as belonging to any known element. 

 Lockyer conjectured that it was due to an unknown gas 

 which he called helium; this gas, as will appear, was subse- 

 quently discovered on the earth, and is found to play a most 

 important part in modern physics. The identification of 

 terrestrial elements in the atmosphere of the sun or stars 

 ultimately proved not such a simple matter as was at first 

 supposed, because the relative intensities of the lines emitted 

 by a luminous body, and sometimes the whole spectrum, 

 changed when the conditions were altered. Lockyer turned 

 this complication to good account by trying to gauge not only 

 the substance itself, but its temperature and physical con- 

 dition in the celestial bodies. He was thus led to his meteoric 

 hypothesis of the formation and subsequent evolution of the 

 solar systems, into which it is not possible to enter here. 



The most memorable discovery with which the name 

 of Huggins is connected is the measurement of the velocity 

 of stellar bodies in the line of sight. A body moving directly 

 towards, or away from, us keeps the same apparent position 

 in the sky, but just as the whistle of a locomotive alters its 

 pitch when, after approaching us, it passes and then moves 

 away, so is the wave of light received by us affected according 



