1885.] on Sunlight and the Earth's Atmosphere. 281 



scale. If it be asked which of these is correct, the answer is " both 

 of them." Both rightly interpreted mean just the same thing, but in 

 the lower one we can more conveniently comi^are the ground of the 

 researches of others with these. These great gaps I was at first iu 

 doubt about, but more recent researches at Alleghany make it probable 

 that they are caused by absorption in our own atmosphere, and not in 

 that of the sun. 



We would gladly have stayed longer, in spite of physical discom- 

 fort, but the formidable descent and the ensuing desert journey were 

 before us, and certainly the reign of perpetual winter around us grew 

 as hard to bear as the heats of the desert summer had been. On 

 September 10 we sent our instruments and the escort back by the 

 former route, and, ourselves unencumbered, started on the adventurous 

 descent of the eastern precipices by a downward climb, which, if 

 successful, would carry us to the plains in a single day. I at least 

 shall never forget that day, nor the scenery of more than Alpine 

 grandeur which we passed in our descent, after first climbing by 

 frozen lakes in the northern shadow of the great peak, till we crossed 

 the eastern ridges, through a door so narrow that only one could pass 

 it at a time, by clinging with hands and feet as he swung round the 

 shoulder of the rocks — to find that he had passed in a single minute 

 from the view of winter to summer, the prospect of the snowy peaks 

 behind shut out, and instantly exchanged for that below of the glow- 

 ing valley and the little oasis where the tents of the lower camp were 

 still pitched, the tents themselves invisible, but the oasis looking like 

 a green scarf dropped on the broad floor of the desert. We climbed 

 still downward by scenery unique in my recollection. This view of 

 the ravine on the screen is little more than a memorandum made by 

 one of the party in a few minutes' halt part-way down, as we followed 

 the ice-stream between the tremendous walls of the defile which rose 

 2000 feet, and between which we still descended, till, toward night, 

 the ice-brook had grown into a mountain torrent, and, looking up the 

 long vista of our day's descent, we saw it terminated by the Peak of 

 Whitney, once more lonely in the fading light of the upper sky. 



This site, in some respects unequalled for a physical observatory, 

 is likely, I am glad to say, to be utilised, the President of the United 

 States having, on the proper representation of its value to science, 

 ordered the reservation for such j)urposes of an area of 100 square 

 miles about and inclusive of Mount Whitney. 



There is little more to add about the journey back to civilisation, 

 where we began to gather the results of our observation, and to reduce 

 them — to smelt, so to speak, the metal from the ore we had brought 

 home — a slow but necessary process, which has occupied a large part 

 of two years. 



The results stated in the broadest way mean that the sun is blue 

 — but meaji a great deal more than that ; this blueness in itself being 

 perhaps a curious fact only, but in what it implies, of practical 

 moment. 



