56 THE BORDERLAND OF SCIENCE. 



underrated the extent of the depression of these regions. 

 The reason of this X. considered to be the refractive 

 power of the dense atmosphere within these depressions, 

 which causes them to appear shallower than they really 

 are, much as a basin when filled with water appears 

 shallower than it really is. We judged the depth of the 

 depression in the case of this particular spot to be fully 

 ten thousand miles. 



Placed as we were now at the borders of an enormous 

 sun-spot, we could understand the real meaning of 

 some of those appearances which had seemed perplexing 

 during the telescopic scrutiny of the sun. In the first 

 place, we could perceive that, .throughout the whole 

 extent of the depression before us, there was the most 

 intense activity; but the most violent action took place 

 all round the borders of the spot. We could see, in 

 fact, that several of the prominences we had observed 

 during our progress sprang from the borders of the 

 relatively dark depression ; and though scarcely a trace 

 remained (to our great amazement) of the mighty 

 eruption we had so lately witnessed, we could judge 

 from the aspect of the region we had reached, that here 

 (on the nearer border of the spot) that tremendous 

 outburst had taken place. All round the spot immense 

 waves of faculce raised their glowing crests above the 

 general solar level ; and we could see that this was due 

 to the action of some cause by which the matter of the 

 photosphere had been driven outwards from the region 

 of the spot, and had so become heaped up in great 

 ridges all round. Descending to a lower level, we found 



