MOUNTAIN OBSURVATORIES. 401 



great gaps produced by absorption somewhere / but, since tliey show 

 no signs of diminution at great altitudes, they are obviously due to an 

 extra-terrestrial cause. Here a tempting field of inquiry lies open to 

 scientific explorers. 



On one other point, earlier ideas have had to give way to better- 

 grounded ones derived from this fruitful series of investigations. 

 Professor Langley has effected a redistribution of energy in the solar 

 spectrum. The maximum of heat was placed by former inquirers in 

 the obscure tract of the infra-red ; he has promoted it to a position in 

 the orange approximately coincident with the point of greatest lumi- 

 nous intensity. The triple curve, denoting by its three distinct sum- 

 mits the supposed places in the spectrum of the several maxima of 

 heat, light, and " actinism," must now finally disappear from our text- 

 books, and with it the last vestige of belief in a corresponding three- 

 fold distinction of qualities in the solar radiations. From one end to 

 the other of the whole gamut of them, there is but one kind of differ- 

 ence — that of wave-length, or frequency in vibration ; and there is but 

 one curve by which the rays of the spectrum can properly be repre- 

 sented — that of energy, or the power of doing work on material par- 

 ticles. What the effect of that work may be depends upon the spe- 

 cial properties of such material particles, not upon any recondite 

 faculty in the radiations. 



These brilliant results of a month's bivouac encourage the most 

 sanguine anticipations as to the harvest of new truths to be gathered 

 by a steady and well-organized pursuance of the same plan of opera- 

 tions. It must, however, be remembered that the scheme completed 

 on Mount Whitney had been carefully designed, and in its preliminary 

 parts executed, at Alleghany. The interrogatory was already pre- 

 pared ; it only remained to register replies, and deduce conclusions. 

 Nature seldom volunteers information : usually it has to be extracted 

 from her by skillful cross-examination. The main secret of finding 

 her a good witness consists in having a clear idea beforehand what 

 it is one wants to find out. No opportunities of seeing will avail 

 those who know not what to look for. Thus, not the crowd of casual 

 observers, but the few who consistently and systematically think, will 

 profit by the efforts now being made to rid the astronomer of a small 

 fraction of his terrestrial impediments. It is, nevertheless, admitted 

 on all hands that no step can at present be taken at all comparable 

 in its abundant promise of increased astronomical knowledge to that 

 of providing suitably elevated sites for the exquisite instruments con- 

 structed by modern opticians. — Edinburgh Review. 



VOL. XXVI. — 26 



