W. A. Nm-ton— Physical Constitution of the Sun. 405 



outer limit of the hydrogen envelope ; and we know that as a 

 matter of fact, the chromosphere, composed chiefly of hydrogen, 

 extends above the photosphere. 



If the products of the surface combustion were all to descend 

 indefinitely into the vaporous photosphere, without undergoing 

 ;her 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 ci*ust 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 un- 

 less the tendency of the heat, that augments with the depth, 

 IS counteracted by the opposing tendency of the increasing gase- 

 ous pressure. By reason of these opposing tendencies it 

 may well happen that there may be a certain region of dis- 

 sociation of limited depth, above and below which decompo- 

 sition would not occur. But it is to be observed that it does 

 not loUow that all of the products of surface combustion as 

 jey pass through such a region would be decomposed ; since 

 t^e reduction of temperature attending eveiy instance of de- 

 composition tends to prevent decomposition of other surround- 

 ing masses in the act of descending. 



-Lms sudden dissociation of large masses of combined 

 elements, though occurring at certain depths within the pho- 

 ospdere it will be seen may eventually play a conspicuous 

 iehi 1^^^^^^®" Unless the region of dissociation should 



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

 lents alter separation will be urged upward by the effective force 

 abov tf °°' ^^°®i^^ rapidly, and emerge with a high velocity 

 ntto- \ . respective envelopes. The ascensional velocities 

 TUp "^ will be greater if large masses are suddenlv decomposed., 

 vp L?^^^®^ ^^ liydrogen set free should attain to the greatest 

 J'^'^y- and rise to the greatest height. They should rise, in 

 thp K °^^^^®S' above the hydrogen envelope, or in other words, 

 l^^^J'^^^osphere. According to Lockyer, in the solar protu- 

 aoKi ?^®' ^^^ ascending hydrogen has in some cases, a velocity 



St,'^oo''Lg" P" ^''""^' ™^ "^" *" ' "^■""^ "' ""'" 



120 rJf'^^*^'^^ J^* ^^ hydrogen, having a projectile velocity of 

 if til? .5 P^^ '^^^nd» shoutd attain an altitude of 43,000 miles, 

 " " ant for that altitude. Some 



,ye , - _ ....^ .^ ,. height of 100,000 miles above 



stancpf ^ Photosphere. Prof. Eespighi, has even noticed in- 

 ot an elevation of 160,000 miles. Such enormous 



