36 LIGHT SCIENCE FOR LEISURE HOURS. 



soon obtained results which supplied most important 

 information respecting the solar constitution. It had 

 been shown long since by Pliicker and Hittorf, that 

 the bright lines which form the spectrum of hydrogen 

 and other gases vary in appearance according to the 

 circumstances of pressure, temperature, and so on, 

 under which the gases give out their light. Here was 

 at once a powerful means of inquiring into the condi- 

 tion of the gases forming the solar envelope. Dr. 

 Frankland was able to conGrm the researches of 

 Pliicker and Hittorf, and further he went far towards 

 proving that pressure is the chief circumstance affecting 

 the appearance of the bright lines of hydrogen and 

 other gases. He showed, too, that with a great dimi- 

 nution of pressure some of the bright lines disappear. 



Now, turning to the sun, Mr. Lockyer was able 

 through these researches to form at least a probable 

 opinion respecting the pressure at which the hydrogen 

 forming the solar prominences in reality exists. He 

 found that the bright lines are so narrow as to indicate 

 a singularly low pressure considering the enormous 

 force with which the sun attracts his atmospheric 

 envelope a pressure actually less, indeed, than that 

 of our own atmosphere. He could trace also the 

 elevations at which some of the lines of the various 

 elements forming the solar atmosphere vanish the 

 others remaining and so, by comparison with Dr. 

 Frankland's elaborate researches, could tell at least 

 with some probability what, is the actual pressure at 

 different heights in the solar atmosphere. It was, in- 



