12 Turner, Total Solar Eclipses. 



to examine a little more in detail what further information 

 this gives us about them. 



But to prevent misconception, I must recur to one or 

 two points which have been omitted so far in order to 

 simplify the statement. When we come to consider the 

 nature of the Corona, we must remember that it is certainly 

 a complex structure. The spectroscope gives us evidence 

 of the existence of gases which show bright lines in the 

 spectrum. One of these, at least, is a gas unknown to us 

 on earth, which has been called coronium. But besides 

 gases, there are in the Corona solid, or perhaps liquid, 

 particles ; for part of the light which comes to us is 

 polarised light, and from the character of the polarisation 

 we can infer the existence of particles of this kind. More- 

 over we learn something of their approximate size ; many 

 of them cannot be very much bigger than a wave length 

 of light, or there would be no such effect. Of course, 

 there maybe larger particles than these in the Corona, but 

 these will not polarise the light, and therefore do but 

 dilute the effect. If we find that the polarisation is 

 strong, this is evidence that the number of large particles 

 is small. We see here how important it is to get an 

 actual measure of the amount of polarisation, and measure- 

 ments of this kind are in progress. We do know, however, 

 that the polarisation is strong, and therefore the small 

 particles numerous, and for the present we are going to 

 consider them alone, as if they constituted the whole 

 Corona. We can afterwards make allowance for the 

 elements neglected. 



But the particles are almost certainly not stationary 

 relatively to the sun ; they are either rising or falling, or 

 rising and falling : and it is into their state of motion 

 that I propose to enquire, in the light of the measure- 

 ment above quoted. 



