Prof, W. A. Norton on the Physical Constitution of the Sun. 65 



decomposition, no further visible effects would ensue. We 

 could only follow with the mind's eye the gradual growth of the 

 central nucleus of the sun, and recognize that we probably have 

 before us a picture of the process by which the materials of the 

 earth's crust were fashioned and accumulated in the earlier ages 

 of its history. But the probability is that the descending 

 masses would eventually arrive at a depth where the higher 

 temperature would effect a dissociation of the combined ele- 

 ments (as Faye supposes). This must inevitably happen unless 

 the tendency of the heat that augments with the depth is coun- 

 teracted by the opposing tendency of the increasing gaseous 

 pressure. By reason of these opposing tendencies it may well 

 happen that there may be a certain region of dissociation of 

 limited depth, above and below which decomposition would not 

 occur. But it is to be observed that it does not follow that all 

 of the products of surface-combustion as they pass through such 

 a region would be decomposed, since the reduction of tempera- 

 ture attending every instance of decomposition tends to prevent 

 decomposition of other surrounding masses in the act of de- 

 scending. 



This sudden dissociation of large masses of combined ele- 

 ments, though occurring at certain depths within the photo- 

 sphere, it will be seen, may eventually play a conspicuous part 

 at the surface. Unless the region of dissociation should lie 

 below that of repulsion for the elements separated, these ele- 

 ments after separation will be urged upward by the effective 

 force of repulsion, ascend rapidly, and emerge with a high velo- 

 city above their respective envelopes. The ascensional velocities 

 attained will be greater if large masses are suddenly decom- 

 posed. The masses of hydrogen set free should attain to the 

 greatest velocity and rise to the greatest height. They should 

 rise in eruptive masses above the hydrogen envelope, or, in other 

 words, the chromosphere. According to Lockyer, in the solar 

 protuberances the ascending hydrogen has in some cases a ve- 

 locity as high as 120 miles per second, and rises to a height 

 of more than 40,000 miles. 



A vertical jet of hydrogen having a projectile velocity of 

 120 miles per second should attain an altitude of 43,000 miles, 

 if the solar gravity were constant for that altitude. Some 

 prominences have extended to a height of 100,000 miles above 

 the sun's photosphere. Professor Respighi has even noticed 

 instances of an elevation of 160,000 miles. Such enormous 

 heights imply either a greater initial velocity than 120 miles 

 per second, or that the full energy of the solar attraction does 

 not take effect on the eruptive masses of hydrogen in the region 

 above the photosphere. From our theoretical point of view we 



Phil. Mag. S. 4. Vol. 42. No. 277. July 1871. F 



