500 KANSAS CITY REVIEW OF SCIENCE. 



entering that their due arrangement and subordination becomes a task well nigh 

 impossible. Difficult also from the magnitude of the operations involved, pres- 

 sures so great and temperatures so high that our terrestrial experiments are but 

 gropings in the dark. We have to measure the sun by a candle. 



The first point to be stated is that by far the greater^part of the Sun is prob- 

 ably in a gaseous condition. That in the photosphere some substances are so 

 far cooled as to become liquid and, may be, solid, there seems to be little doubt; 

 but the central body, the chromosphere, part of the photosphere, and part of the 

 corona are considered to be gaseous. It is generally believed that the gases 

 composing the central part cannot act as do gases on earth ; the density of the 

 sun, the pressure consequent upon its great mass, and the temperature necessary 

 to keep up the observed radiation, all producing results that modify the general 

 properties of the gases. They " would be denser than water, and, since, as Max- 

 well and others have shown, the viscojgity of a gas increases fast with rising tem- 

 perature, it is probable that it would resist motion something like a mass of pitch 

 or putty, "f That the chromosphere and its prominences and some parts of the 

 corona are in a gaseous condition, the spectroscope abundantly proves. 



The supposition of the gaseous condition of the Sun enables us to explain 

 some known facts. It is within reason to suppose that the pressure and tempera- 

 ture can be so combined as to produce the known density of the Sun. In fact, 

 if we but knew that there is but one element in the Sun, and what that element 

 is, we could calculate the temperature from the known density and pressure. 



The source of the energy radiated by the Sun and the manner of its radia- 

 tion are readily explained on this gaseous hypothesis. The light and heat may 

 come from one or both of two sources, (i). g a,ses and vapors so condensed 

 as to give continuous spectra; (2) matter that has cooled below its boiling point 

 and has consequently become liquid or solid. It will be seen that the latter is 

 the more probable condition of affairs. The supply of energy is explained ac- 

 cording to the well known fact of the heating of a gaseous sphere by the contrac- 

 tion caused by cooling. It is estimated that a reduction of the solar diameter 

 220 feet per annum would produce the present radiant energy. It is quite prob- 

 able, however, that this contraction is not the only source of the Sun's heat, for 

 the impact of meteors cannot fail to set free an immense amount of energy. 



Again by admitting that the sun is gaseous rather than solid — the latter sup- 

 position was made by Herschel and is held by Zollner and hinted at by Spoerer — 

 the unequal times of rotation at different latitudes can be considered as possible ; 

 so far as 1 know, however, no adequate explanation of this phenomenon has yet 

 been advanced. 



To explain the phenomena seen at and near the visible surface of the sun it 

 becomes necessary to localize certain actions that are supposed to take place in 

 that region. Briefly it is supposed that the region which we call the photosphere 

 is so cool in comparison with the central parts that its temperature is below the 



+ The Sun ; page 286. 



