THE PROGRESS OF SCIENCE. 



95 



of its atmosphere, would radiate into 

 space twice as much energy as at the 

 present time. He also showed that an 

 increase of 25 per cent, in the absorp- 

 tion by the solar envelope would lower 

 the surface temperature of the earth 

 by 100°F. Langley's attention was 

 directed chiefly to the earth, and not 

 to the reflex action on the sun itself, 

 which such an atmosphere must exert. 

 A decrease in the outside radiation of 

 energy, caused by any change in the 

 enclosing solar envelope, means an in- 

 crease in the energy contained in the 

 sun. It is reasonable to assume that 

 changes in the absorptive power of the 

 atmosphere must arise, and Mr. Hahn 

 presents the query: What becomes of 

 the energy which is prevented from 

 escaping into space by the solar 

 envelope? He endeavors to show that 

 there may occur in the atmosphere 

 changes sufficient to lead to alterations 

 in the thermal conditions of the sun's 

 mass and attempts to decide how far 

 such changes may lead to the known 

 variations in the phenomena at the sur- 

 face of the sun. Astronomers are gen- 

 erally agreed in accepting the theory of 

 Helmholtz, which accounts for the gen- 

 eration of the sun's heat by the con- 

 traction of its mass. This theory, 

 while it explains the generation of 

 heat in any star, does not in itself give 

 information as to whether the amount 

 of heat thus formed is just sufficient to 

 balance that which is lost by radiation. 

 As a fact, there are doubtless suns, as 

 indicated by the spectroscope, which 

 are increasing, and others which are 

 decreasing, in temperature, and in the 

 life of each sun there is, probably, 

 a period of increasing, and later one 

 of decreasing, temperature. Our sun is 

 perhaps an example of those stars in 

 which the heat lost by radiation is 

 greater than that gained by contrac- 

 tion. With this assumption the layer 

 of maximum incandescence and radia- 

 tion will be shifted nearer and nearer 

 toward the sun's center. The result 

 will be that, due to the increased 



absorption of the denser envelope, the 

 solar radiation will be decreased, 

 which will tend to raise the tempera- 

 ture of the inner layers of the sun 

 itself. By this overheating the vertical 

 temperature-gradient will become so 

 steep that mechanical equilibrium will 

 be impossible. Although retarded by 

 the powerful convection currents which 

 prevail, disturbances will sooner or 

 later ensue as a result of these strained 

 conditions of the internal overheating, 

 and solar outbursts will occur. Mr. 

 Hahn then proceeds to an analytical 

 demonstration. 



The problem consists in determin- 

 ing the changes in the amount of 

 the outside radiation, caused by in- 

 creased or decreased absorption. The 

 method is an application of the Bou- 

 guer-Lambert formula for the ex- 

 tinction of light and heat in an absorb- 

 ing medium. Formulas have been 

 derived for the energy of radiation 

 from the upper limits of the atmos- 

 phere, for the changes in the radiating 

 power, and for the frequency of erup- 

 tions and spots. The results thus ob- 

 tained appear to be in close agreement 

 with observation. The object of the 

 article is to give an abstract of the 

 main principles upon which is built a 

 new solar theory. In a paper which 

 is to appear in the Annals of the Edin- 

 burgh Royal Observatory the author 

 will enter more in detail into the vari- 

 ous applications of the theory to 

 periodic phenomena at the sun's sur- 

 face. This theory differs from the 

 views generally accepted, in that it in- 

 volves the assumption that an increase 

 in the dynamical forces at the surface 

 of the sun indicates a decrease in the 

 heat and light radiation, but here also 

 the author believes that his theory 

 accords well with the facts of observa- 

 tion. 



SCIENTIFIC ITEMS. 



The National Academy of Sciences 

 held its annual stated session at Wash- 

 ington, beginning on April 15. — The 

 spring meeting of the Council of the 



