Tiro YEARS LATER. 37 



fact, much as though an observer on the sun could see 

 our barometric columns standing at a height of thirty 

 inches at the sea level, and at lesser and lesser heights 

 at greater and greater elevations. Precisely as such 

 an observer, supposing him to be acquainted with the 

 nature of the barometric column, could tell the circum- 

 stances of pressure at different heights in our atmo- 

 sphere, so Mr. Lockyer, knowing the gases which form 

 the chromosphere, and informed by Frankland's re- 

 searches of the interpretation of the vanishing of bright 

 lines, could tell the variations of pressure at different 

 heights in the solar atmosphere. 



I have said, however, that the result was not 

 absolutely certain. It is easy to see why this is. 

 Temperature has an undoubted effect upon the bright 

 lines belonging to the gaseous spectra, and it is obvious 

 that the heat throughout the solar atmosphere must 

 far surpass any which our chemists can artificially 

 produce in their laboratory experiments. So that it 

 must still remain open to some question whether we 

 can reason quite so confidently respecting the condition 

 of things in the sun's neighbourhood, as we might if 

 such peculiar relations did not necessarily exist there. 



But at present it seems at least a probable inference 

 that the gases forming the prominences are not sub- 

 jected to very great pressure. And this brings me to 

 the consideration of the phenomena which will un- 

 doubtedly occupy the chief attention of observers 

 during the approaching total eclipse of the sun. When 

 the sun is quite concealed from view by the interposing 



