August 3, 1882] 



NATURE 



315 



solar constant) had been under-estimated by the methods 

 of previous observers, and that conclusions of importance 

 connected with the temperature of the planet remained 

 to be drawn, it became desirable to verify these results, 

 obtained near the sea-level, by direct simultaneous obser- 

 vations at the base and summit of a very high mountain. 



The generosity of a citizen of Pittsburg had provided 

 the special apparatus devised for the new methods, but 

 this was too elaborate to be easily moved to a distant and 

 elevated station. Upon the bearing of the contemplated 

 observations on practical problems of meteorology be- 

 coming known to Gen. W. B. Hazen, the Head of the 

 U.S. Signal Service, he kindly offered to facilitate the 

 transportation of an expedition from the Alleghany Ob- 

 servatory to the Western Territories ; for no wholly 

 suitable site presented itself, save in regions where the 

 aid of the army might be desirable both for transporta- 

 tion and escort. 



With the consent of the trustees of this Observatory, 

 the offer was gladly accepted, and the expedition, which, 

 as originally planned, was a private one, proceeded with 

 material aid from the Signal Service ; and under the 

 advantage of Gen. Hazen's official direction I am enabled, 

 by his kind permission, to here briefly indicate its main 

 objects and results, in advance of a full publication of 

 them, which will shortly be made. 



The site selected, on the suggestion of Mr. Clarence 

 King, and after conference with officers of the Army and 

 Coast Survey familiar with the western wilderness, as 

 suited to the special observations (which made both great 

 altitude and great dryness desirable), was Mount Whitney 

 in the Sierra Nevada of Southern California, It rises to 

 nearly the height of Mont Blanc from one of the most 

 arid regions in the world, and so abruptly, that two 

 stations can be found within easy signalling distance, 

 whose difference of elevation is over 1 1,000 feet. It is, 

 however, on the other side of the continent, in an imper- 

 fectly explored region, and as very little was known of the 

 possibility of carrying such apparatus as ours to the 

 summit, a military escort was provided, on the con- 

 tingency of our being obliged to occupy some site still 

 more remote from civilisation. 



The scientific members of the party, consisting of Capt. 

 O. E. Michaelis, of the Ordnance, of Messrs. J. E. Keeler 

 and W. C. Day, civilian assistants, and the writer, started 

 from Pittsburg on July 7, for a railroad journey of over 

 3000 miles, which was greatly facilitated by the courtesy 

 of Mr. F. Thomson, of the Pennsylvania Company, which 

 enabled the writer to take all the apparatus with him in a 

 special car. At San Francisco, after some delay, which 

 the kindness of General M'Dowell, commanding the de- 

 partment of the Pacific, enabled us to pass agreeably, 

 the escort was provided, and the party joined by Mr. 

 George Davidson and two Signal Service non-commis- 

 sioned officers. With these it proceeded to a point about 

 400 miles further south (Caliente), where we exchanged 

 the swift motion and the comforts of the Pullman car, for 

 the sharp contrast of a route which commenced (with the 

 shade thermometer registering 1 io° F.) by a slow journey 

 across the Inyo Desert, shadeless and waterless, for one 

 hundred and twenty miles. We reached, at the close of 

 the month, Lone Pine at the foot of the Sierras, where a 

 camp was made, to be occupied as a lower station, and 



where the instruments were set up. Among these was a 

 massive siderostat, sending a horizontal beam to a specially 

 constructed spectrometer, an instrument larger than the 

 one which usually bears the name, and in which the eye 

 is replaced by a bolometer, so adjusted as to measure the 

 heat separately in any ray of the visible and the invisible 

 spectrum. When these measures are repeated at an 

 altitude so great that the total atmospheric absorption is 

 markedly different, we are enabled to determine the rate 

 of this absorption for each ray, and, inferentially, to place 

 the observer wholly outside our atmosphere, and to recon- 

 struct the whole spectrum with the hitherto unknown dis- 

 tribution of energy which must exist there. This was 

 used in connection with actinometers, pyrheliometers, 

 and the u;ual instruments for such a research ; but the 

 problem of the safe transportation of the larger apparatus 

 to the summit of Mount Whitney, which now rose above 

 us in a seemingly perpendicular wall of granite, here pre- 

 sented itself in its full difficulty. Our final destination at 

 the summit was in the clearest view, for the extraordinary 

 dryness of the air and the absence of all aerial perspective 

 made the mountain seem so near, that it wore the aspect 

 of a quite neighbouring pile of lofty and moss-covered 

 gray rock, patched with white, and of a wildly jagged out- 

 line (the " Sierra ")• This white (which we knew to be 

 large snow fields), and the use of the telescope; which 

 resolved the "moss" into great forests, dispelled the 

 illusion, and we realised the obstacles we had to surmount. 

 A preliminary exploration showed that the ascent was 

 difficult, and with such apparatus as ours impossible ; a 

 long detour was therefore necessary to avoid the precipices 

 on the eastern front, and our mule trains were in fact 

 occupied from seven to eight days in reaching a point 

 below the summit actually but sixteen miles distant. We 

 traversed in the ascent a trackless wilderness, climbing 

 what seemed utterly impracticable stony heights ; down 

 which, once or twice a mule lost his footing and rolled 

 with his scientific freight, but over which, though by such 

 a way as siderostats and telescopes probably never tra- 

 velled before, all finally passed with a degree of safety 

 beyond our hopes. 



We had come here to determine (among other objects) 

 what part of the surface temperature of the planet was 

 due to the sun's direct radiant heat, and what part to the 

 effect of the earth's atmosphere in storing this heat. 



It was interesting then, if not wholly agreeable, 'to 

 repeat the experience of former observers in our own 

 persons, and to notice that as we ascended and the air 

 grew colder, the sun grew hotter, till our faces and hands, 

 browned as they already were by weeks of sunshine 

 below, were burned anew, and far more in the cold than 

 in the desert heat. As we still slowly ascended, and the 

 surface-temperature of the soil fell to the freezing-point, 

 the solar radiation became intenser, and many of the 

 party presented an appearance as of severe burns from 

 an actual fire, while near the summit the temperature in 

 a copper vessel, over which was laid two sheets of plain 

 window glass, rose above the boiling-point, and it was 

 certain that we could boil water by the direct solar rays 

 in such a vessel among the snow-fields. 



It is possibly worth remark that owing to the dryness 

 of the air, though isolated snow-fields lay above and 

 below us, the ground we travelled over was bare, and it 



