SOLAR THEORIES. 501 



boiling point of some substance (probably of the carbon group), and that this sub 

 stance is in a liquid or solid state, being cooled as masses of vapor rise from the 

 interior. This cooling comes from both radiatioii and expansion. When suffici- 

 ently cool to appear dark in comparison with the hotter droplets, it forms a 

 a cloudlike layer of smoke. It must be borne in mind that the bright droplets 

 and darker smoke particles are floating in an atmosphere of the vapors of other 

 metals; for the temperature is above the boiUng point of all elements but the one 

 supposed. The supply of liquid droplets is easily accounted for by supposing that 

 the smoke particles are continually raining down through the region of cooling 

 and, after being heated in the interior, are again forced upward, again liquified, 

 and again become smoke. White light is given out by the drops of molten mat- 

 ter and, during its course through the incandescent vapors in which these drops 

 float, is robbed of certain rays chosen by those vapors ; while in passing through 

 the smoky layer general absorption takes place. This conception, first fully 

 elaborated by Prof. Hastings,* explains satisfactorily many known facts. The 

 mottled appearance of the Sun's surface, the general absorption with its promi- 

 nent increase near the limbs, the selective absorption and its very feeble modifica- 

 tion at the limbs, faculae, sun spots, and some puzzling questions of solar spectro- 

 scopy, all yield readily to its influence. As an explanation of photospheric phe- 

 nomena the theory seems to be quite satisfactory, but its province is hmited. 



The condition of affairs in the chromosphere, the formation and nature of the 

 prominences, the velocities with which the matter that composes them is forced 

 upward, the nature and condition of the atmosphere in which they are, their 

 density and temperature, these are questions that have, as yet, no satisfactory 

 answers. 



And what of the corona ? It has been conjectured that it consists of matter 

 ejected from the Sun and kept in suspense by electrical repulsion; that there is a 

 constant supply of this ejected matter ; that there is an exceedingly attenuated at- 

 mosphere of gas surrounding the Sun and through it clouds of meteors follow 

 their orbits obedient to the law of gravitation. The truth is that the only facts 

 that we know are that it is partly gaseous and partly solid (or liquid) and that its 

 density is very small indeed. Beyond these, conjecture has supreme control. 



We may say, then, that in all probability the Sun, as a whole, is gaseous ; 

 that the photosphere is a region of liquefaction and solidification ; that we know 

 but little about the prominences; still less about the corona; and that our igno- 

 rance of solar dynamics is almost perfect. 



* American Journal of Science and Arts. Third Series, Vol. XXI, page 33. 



