OCTOBEE 11, 1895.]' 



S'CmNCK 



485 



the report of the committee of ten ap- 

 pointed by the National Educational Asso- 

 ciation upon the courses of instruction in 

 secondary schools. 



Dr. Edmund J. James, professor of pub- 

 lic finance and administration in the Whar- 

 ton School of Finance and Economy, and 

 professor of political science in the graduate 

 department of the University of Pennsyl- 

 vania, has accepted the professorship of 

 public administration at the University of 

 Chicago. 



Richard E. Dodge, of the department of 

 geography in Harvard University, has been 

 appointed instructor in geography and geol- 

 ogy in the Teachers' College, New York. 



The University of Pennsylvania expects 

 an increase in the number of students in 

 almost every department. The Freshman 

 Class in the medical school numbers about 

 250, and the upper classes include 50 stu- 

 dents from other institutions. 



Dr. Arthur D. Frizell has been ap- 

 pointed associate professor of mathematics 

 in the University of the City of New York. 



COBBESFONDENCE. 



THE ABSORPTION OF TERRESTRIAL RADIATION 

 BY THE ATMOSPHERE. 



In the issue of Science for August 16th Pro- 

 fessor Hallock's account of Langley's bolometric 

 studies contains the following statement : ' ' Our 

 atmosphere acts like a valve, transmitting in 

 almost undiminished strength the short quick 

 waves of energy radiated to us from the sun, 

 but refusing absolutely to return the long slow 

 waves in which the earth tries to radiate the 

 energy back into space. Without this atmos- 

 phere we should all have been frozen long 

 ago" (p. 178). 



■ This leads to an interpretation of Langley's 

 results so different from that which I have gath- 

 ered from his writings that a brief comment on 

 the subject seems desirable. It seems to me 

 that.Langley has shown that the solar rays. find 



the atmospheric valve badly clogged when they 

 attempt to pass inward through it, and that the 

 terrestrial rays find the valve very leaky when 

 it tries to prevent their passage outward. . 



In the first place, regarding the entrance of 

 solar rays, Langley found from his observations 

 at Allegheny and Mt. Whitney that about half 

 their energy is lost in passing down through 

 clear air. He drew a curve to represent the 

 distribution of energy in the spectrum of the 

 high sun at Allegheny ; the area included be- 

 tween the curve and its horizontal base line cor^ 

 responding to 1.7 on a scale of calorics. Aut 

 other curve was constructed on the same base, 

 but with ordinates representing the inferred 

 distribution of energy in the solar spectrum out- 

 side of the atmosphere ; the area here included 

 corresponding to 3.5 calorics (' Researches on 

 Solar Heat,' Prof. Papers, U. S. Signal Service,. 

 XV., p. 144 and pi. XV.). Later statements 

 increase the average percentage of transmission 

 of the solar beam to 10 fc (' The Temperature 

 of the* Moon,' Mem. Nat. Acad. Sciences, 1888, 

 IV., 89); but a valve that could, when open, 

 allow only 70 ^ of a current to pass through it 

 would be regarded as a very imperfect mechan- 

 ism. 



In the second place, the action of the atmos- 

 phere on rays emitted from the earth is inferred 

 chiefly from its action on rays emitted by the 

 moon and by experimental radiators. The 

 moon's spectrum is shown to consist of two 

 parts ; one part being simply reflected sunlight 

 with its maximum energy in rays of ' luminous ' 

 wave-lengths ; the other part being true lunar 

 rays, emitted by true lunar radiant action, with 

 their upper and lower limits at wave-lengths of 

 one and perhaps fifty a", and their maximum 

 energy in wave-lengths of seven ,". These lat- 

 ter are in a spectral region of which no one 

 had any knowledge whatever before Langley's 

 studies about 1886. The solar rays, infra-reds 

 as well as luminous and ultra-violet rays, are 

 transmitted by glass, but the true lunar rays 

 are entirely cut off by glass and must be studied 

 with rock-salt prisms. The ratio of the energy, 

 of the solar rays reflected by the moon to that 

 of the true lunar rays is as one to seven (Mem. 

 N. A. S., IV., 197; or Amer. Joum. Science, 

 Dec, 1889, 435), . As is the. case with the xaya 



