414 THE CHEMISTRY OF THE SUN. [CHAP. 



by the lengths of the various lines. The stratum which reaches 

 highest up has a spectrum containing a certain line of mag- 

 nesium. The next, which is shallower, consists of a substance 

 about which we know nothing, except that its line is called 

 " 1474." Then "we get other shallower strata. These, again, 

 are of unknown origin. The lower we go, the deeper does the 

 mystery become. 



(3) Quiet prominences. The next degree of disturbance shows 

 itself in a different way, but very frequently in a region where 

 the first beginnings of a disturbance of the temperature equi- 

 librium, produced by falling material, had been evidenced in 

 the manner just described ; we get the formation of what is 

 called a quiet prominence. 



As a rule they need not be very high. By very high I mean 

 40,000 miles. And these quiet prominences may also last for a 

 very long time. Many of them resemble trees. I was fortunate 

 enough to be one of the early observers of these exquisite 

 forms, which one never gets tired of looking at, and the first 

 time I saw one I wrote down in my note-book that the chromo- 

 sphere and prominences in that place reminded me of an Eng- 

 lish hedge-row with luxuriant elms. The lower part of the 

 chromosphere, of course, represented the hedge, and the pro- 

 minences the elms. The simile of a hedge with trees in it was 

 not at all a bad one, but some years afterwards I found a very 

 much better one, which is perhaps nearer the truth of Nature. 

 It was my duty in the year 1878 to go to America to look at an 

 eclipse. I crossed the Atlantic in the high summer, and we 

 naturally had to pass through a considerable amount of fog. 

 We were three days in a dense fog, and one of the delightful 

 things about that fog was that one day we were steaming 

 through an opening, and saw its edge, which was apparently 

 upright and solid, about a mile off, and we coasted along it. 



I found that the fog was fed by what I at once called 

 fog-spouts. Everybody knows what water-spouts are, and we 



