802 



SCIENCE. 



[N. S. Vol. XX. No. 519. 



(b) solar energy converted in the upper at- 

 mosphere into heat. 



2. The functions of these two sources were 

 separate. Earth-heat controlled the surface 

 temperatures during its prevalence, and by 

 the laws of cooling solids was uniformly dis- 

 tributed at sea level; it was held near the 

 planetary surface by the enshrouding media, 

 by which it was trapped and through which 

 it escaped slowly, not by direct radiation, but 

 by the performance of work, namely the evap- 

 oration of water, and by convection currents 

 which carried warm air to the upper regions 

 of the atmosphere, from which regions only 

 could free radiation of heat into space take 

 place. Solar energy did not directly afPect 

 surface temperatures, during the existence of 

 earth heat as a sensible factor, by reason of 

 the intervention of a dense cloud-sphere in- 

 cident to the universally warm oceans whose 

 temperature is attested by early fossil life; 

 but during this period solar energy acted as a 

 conservator of planetary heat by warming the 

 upper regions of the atmosphere and clouds. 



' 3. Under these conditions, lower and lower 

 temperatures supervened and were recorded 

 by fossil life and ice action distinctly non- 

 zonal in distribution, but varying locally 

 through wide ranges by reason of differences 

 in elevation. 



4. Land areas reached glacial temperatures 

 whenever and wherever they were thrust up 

 above a snow-line controlled by earth heat, 

 and such snow-line was in the main contin- 

 uously lowered but may have fluctuated and 

 was independent of latitude until the culmi- 

 nation of the ice-age; land areas reached gla- 

 cial temperatures earlier than ocean areas, 

 by reason of the low specific heat of earth 

 and rocks, their more intense rate of radia- 

 tion, through the cooling action of rain and 

 snow and by reason of greater elevation, and 

 they were subjected to maximum giaciation 

 along lines of maximum precipitation, and 

 may have escaped all but light local giaciation 

 in regions of minimum cloud formation and 

 precipitation. 



5. Upon the cooling of the oceans, the effec- 

 tive remnant of earth-heat was exhausted and 

 cloud formation reached a minimum, permit- 



ting solar energy to reach the surface arid to 

 assume domination and control of its tem- 

 peratures; the climates of such contl-ol be- 

 came zonal by reason of direct exposure to a 

 zonally distributed source, and these climates 

 gradually rose in temperature by reason of 

 the trapping of heat rays emitted by the 

 warming planetary surface; such rise is yet 

 in progress as recorded by retreating glaciers 

 and advancing plant and animal life. 



6. These progressive changes of climate 

 have been in harmony with the principles of 

 climatic evolution herein set forth; and the 

 principles are substantiated by the facts of 

 geology and by the phenomena now taking 

 place. 



Mr. 0. G. Abbot, of the Astrophysical Ob- 

 servatory, under the title ' Radiation and Ter- 

 restrial Temperature,' discussed the substan- 

 tial equilibrium of temperature of the earth, 

 and consequent equality of solar radiation 

 absorbed in and about the earth to that emit- 

 ted from and about the earth to space. After 

 speaking of the great complexity of the earth 

 and atmosphere as an absorber and radiator, 

 certain maximum and minimum values of the 

 solar constant and of the possible terrestrial 

 temperature were obtained by considering the 

 substitution of a black body or perfect radia- 

 tor for the earth. In this way it was shown 

 that the solar constant can not exceed 3.88 

 calories, and may be indefinitely below this 

 according as the earth reflects less than 44 

 per cent, of solar radiation, or radiates to 

 space less perfectly than a black body. Tak- 

 ing 1.9 calories as the minimum allowable 

 assumption of the solar constant, it was shown 

 that the mean temperature of the earth would 

 remain above — 33° C. if the earth were a 

 perfect radiator and the reflection of solar 

 rays did not exceed 44 per cent. Accordingly 

 we owe not exceeding 58° rise of temperature 

 to the imperfect radiation of the earth. But 

 in the absence of clouds the mean earth tem- 

 perature would certainly exceed 0° C. It ap- 

 peared that if the temperature of the oceans 

 could be raised 25° 0. the cloudiness would 

 so far increase as to make giaciation of 

 the land a probable consequence. Professor 

 Arrhenius's carbonic acid theory of glacia- 



