THE RECENT ECLIPSE OF THE SUN. 21 



large parts of its surface without spills, or that the spills over many 

 such parts must be very short. "When this consideration is attended 

 to, the spillikin corona will be found to have a very complex and re- 

 markable figure. 



It is not to be wondered at that, so soon as the corona began to be 

 thought about at all, astronomers were led to believe that it is not of 

 the nature of a solar appendage, but either a sort of halo in our own 

 atmosphere, or else an appendage belonging in some way to the moon. 

 Kepler and Halley and Newton, to say nothing of a host of other as- 

 tronomers who considered the question during the infancy of modern 

 astronomy, were led to different conclusions, by the comparatively im- 

 perfect evidence available in their day. We may pass over the argu- 

 ments adduced in favor of the three several theories which were in 

 question. Suffice it that, gradually, it was admitted more and more 

 generally that the corona must be some appendage surrounding the 

 sun ; and, in comparatively recent times a quarter of a centuary ago, 

 or thereabouts the opinion began to prevail that the corona is in fact 

 the sun's atmosphere. 



But quite recently discoveries were made which seemed to throw 

 great doubt upon this opinion. By means of the instrument called the 

 spectroscope, astronomers have learned not only how to study the sun's 

 colored prominences when the sun is shining in full splendor, but also 

 to determine to some extent the condition of the glowing gas of which 

 those prominences are formed. When this was done, it did not ap- 

 pear that the density of the glowing gas even close by the sun's body 

 was so great as might be expected if the corona were an atmosphere 

 properly so called. Some prominences are shown in the figure ; and 

 if we consider the pressure to which objects so placed must be sub- 

 jected, supposing them to lie at the bottom of an atmosphere more 

 than a million miles in height, we shall at once see that the pressure 

 of our own air at the sea-level would be a mere nothing by compari- 

 son. It is supposed that our air may be two or three hundred miles 

 in depth, but, even if we suppose it to be ten times as deep as this, the 

 depth of the imagined solar atmosphere would be many times greater. 

 And then the pressure of our air is caused by the earth's attraction, 

 and would be greater if the earth exerted a greater attraction. But 

 the attractive energy of the sun (at his surface) exceeds the force of 

 the earth's gravity about twenty-seven times. "We may safely infer, 

 then, that an atmosphere such as the corona was supposed to be, would 

 cause a pressure exceeding the atmospheric pressure we experience 

 some thousands of times. The gas forming the prominences would 

 be correspondingly compressed under these circumstances. But as a 

 matter of fact the pressure at the very base of the colored promi- 

 nences appears to be a mere fraction of that which our own air exerts 

 ftt the sea-level. 



Accordingly, Mr. Lockyer, who had taken a prominent part in es- 



