A NEW SOLAR 'PITKOKY." 



By Prof. J. Halm, 



Jioi/dl OliHcrnUoi'i/, I'jJiHhiin/li. '' 



It i.s a r(.Miiaiktit)k' fact that in the numerous theories wliieli have 

 been propounded in explanation of the periodic changes of the sohir 

 ])henoniena no account has yet been taken of so important an ehMuent 

 as the light and heat absorbing- envelope surrounding the photosphere. 

 The attention which this so-called solar atmosphere has hitherto 

 received, on the part even of our most eminent in^•estig■ators, in con- 

 nection with the econom}" of radiant enei'gv on our luminary, is utterly 

 disproportionate to the importance of the suljject. In spite of the fact, 

 which was first accurately estal)]ished by Langley's oliservations and 

 was afterwards confirmed by others, that the sun, if deprived suddenly 

 of this protecting screen would radiate into space as much as double 

 its present amount of energy, solar physicists failed to perciMve that 

 changes in the absorptive power of this envelope must entail conse- 

 quences of the most far-reaching chiiracter with respect to the thermal 

 conditions on and in the sun. That such changes — and these, too, of 

 no inconsideral)le magnitude — must inevitabh^ occur, is a conclusion 

 which it is hardly possi})le to evade when it is rememliered that the 

 supreme control over the dispensation of solar energy depends entirely 

 on a thin, shallow surface layer, the matter of which is constantly 

 tossed about by vehement eruptions and acted upon ])y a most com- 

 plicated and pow^erful system of convection currents to and fi-oni the 

 sun's center. 



The possil)ility of variations of the opacity of the solar atmosphere 

 was, it is true, strongl}- urged, more than twenty years ago, by one 

 of the greatest authorities on this ([uestion. Shoi-tly aft(>r his well- 

 known res(>arches into the a})sorbing faculty of tiie solar envelope, 

 Langley pointed out the decisive inilnence on the sun's I'adiation into 

 space caused l)y changes in the transmissive power of its atmos[)here. 



"Reprinted, with additiouH by the author, from Nature, No. U)85, voL 85, Fel)ruary 

 13, 1902. 



'> Abstract of a paper in Astr. Nachr. (No. 3728, 3724) : "lTel)er eine neue Theoric zur 

 Erklilrung der Periodicitiit der solaren Erscheinungen." 



160 



