267 



gaseous medium. Tlii.s is a great [)livsi('al [u-obiem, toward the 

 complete solution of which only the first steps are as yet being- 

 made^); but awaiting the linal leyidty of such investigations, we 

 may already atteujpt to api)iy our present knowledge ot' the -matter 

 to the interpretation of solar phcnon)ena. 



From the astropliysical point of view one of the questions material 

 to the case is: what can be presnmed about the general i-adial 

 gradient of the density in the layers we are concerned with? 



This subject has been treated very fully and ingeniously, on the 

 basis of thermodynamics, by Emukn in his book "Gaskugeln." Emukn 

 arrives at the conclusion already mentioned above, that the fall of 

 the densit}^ must be extremely rapid ; but the inference is open to 

 doubt, for in his calculations Em den presupposes gravitation to be 

 the oidy radial force acting ' on solar matter. According to the 

 present state of our physical knowledge, however, we decidedly 

 must admit that on the sun gravitation is counteracted by the pressure 

 of radiation, and by the emission of electrons and perhaps of other 

 chai'ged particles. 



Basing on purely theoretical grounds an estimate of the intensitj^ 

 of that counteraction would, for the present, be as rash as denying 

 its existence ; but some evidence in favour of its essentiality is given 

 by the fact, that many solar phenomena are much better understood 

 if we assume a radial gradient many times smaller than the one 

 that would correspond to gravitational conditions only. In this 

 connection we w^ould call attention to the puzzling properties of 

 quiescent, hovering prominences. Father Fenyt, in his interesting 

 discussion of the long series of prominence observations made at 

 Haynald Observatory, Kalocsa"), is very positive in his assertion that 

 several well-established facts concerning quiet prominences can only 

 be accounted for, if in the solar atmosphere gravity is reduced, by 

 certain repulsive forces, to a small fraction (something of the order Yso) 

 of its commonly accepted value. 



Our hypothesis, that a similar counteraction, opposing the effect 



1) Rayleigh, Phil. Mag. [5] 47, 375, 1899. 



A. Schuster, Astrophysical Journal 21, 1, 1905. 



H. A. LoRENTZ, The theory of Electrons, Leipzig 11)09. 



L. Natanson, Bulletin de racadómie des sciences de Cracovie, .\viil 1907, 

 Décembre 1909. 



W. H. Julius, Physik. Zeitschr. 12, S. 3^9 und 674, 1911. 



L. V. King, Phil. Trans. Roy. Soc. London, A 212, 375, 1912. 



~) Publikalionen des Haynald Observatoriums. Heft X, 138, (1911). Gf. also 

 FÉNYi, Ueber die Holie der Sonnenalmosphüre. Mem. Spellr.ilal. (2), 1, 21, (J 912). 



