l8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. g2 



measurements of the percentage of carbonic acid in the atmosphere. 

 Besides all these, even other types of measurements were made in 

 profusion at Lone Pine, at Mountain Camp, and to some extent on 

 the peak of Mount Whitney. The reduction of this immense mass of 

 evidence was a task which occupied Langley's small force for two 

 years, though it included the immortal Keeler and the assiduous Very. 

 The great object was to determine the transparency of the atmosphere 

 with such certainty, by these operations in one of the purest atmos- 

 pheres of the world, as to fix the value of the solar constant of radia- 

 tion. Langley thought to check the determination by computing from 

 the results at Lone Pine what ought to be found on Mount Whitney. 

 No less than a fifth of the atmosphere lay between these observing 

 stations. Unfortunately Langley was misled by this apparently rea- 

 sonable idea. For at Lone Pine he measured the average transparency 

 for all atmospheric layers to the limit of the atmosphere, a trans- 

 parency obviously greater than that of the more humid and dusty 

 layers between him and Mountain Camp. He could not fairly use 

 his average results at Lone Pine to compute, as he did, what ought 

 to be observed at Mountain Camp. By this error of logic, aggravated 

 by a moderate plus error in the absolute readings of his actinometers, 

 Langley persuaded himself that the Mount Whitney Expedition indi- 

 cated 3.07 calories per square centimeter per minute as the solar con- 

 stant of radiation, a value more than 50 percent too high. His justly 

 great authority maintained this erroneous value for more than 20 

 years. 



But it is not this unfortunate aspect of the reduction of Mount 

 Whitney observations, but the tremendous driving power and fertility 

 of invention of this astonishing pioneer that should fix our attention. 

 He practiced for the first time what the problem demanded, namely : 

 occupation of a high-level desert station, observations of both total 

 radiation and homogeneous rays, and their combination after a definite 

 method. These essentials are still the basis of solar-constant work. 

 He traced and accurately outlined the energy spectrum of the sun far 

 beyond all previous observers. He obtained for the first time accurate 

 transmission coefficients for homogeneous rays. In short, Langley 

 by the Mount Whitney Expedition set up the ideal toward which all 

 later observers strive to approximate. 



"THE TEMPERATURE OF THE MOON" 



" That the moon gives light, but no sensible heat, has been a 

 matter of observation even by the unaided senses of the primitive man, 



