496 



Prof. S. Arrhenius. 



[June 2, 



product of the slowly changing elements uranium, thorium, or 

 actinium present in pitchblende. It was arranged that Mr. Soddy 

 should examine whether radium is produced from uranium, but the 

 results so far obtained have been negative. 



I have taken solutions of thorium nitrate and the " emanating 

 substance " of Giesel (probably identical with the actinium of Debierne) 

 freed from radium by chemical treatment, and placed them in closed 

 vessels. The amount of radium present is experimentally determined 

 by drawing off the emanation at regular intervals into an electroscope. 

 A sufficient interval of time has not yet elapsed to settle with certainty 

 whether radium is being produced or not, but the indications so far 

 obtained are of a promising character. 



" On the Electric Equilibrium of the Sun." By Svante Arbhenius. 

 Communicated by Sir William Huggins, Pres. K.S. Eeceived 

 and read June 2, 1904. 



In recent years many attempts have been made to apply the 

 pressure of radiation, that is a consequence of the theories of Maxwell 

 and Bartoli, to the explanation of cosmical phenomena. Especially the 

 enigma of the nature of comets' tails has been elucidated from this new 

 point of view. 



In a memoir presented to the Swedish Academy of Sciences in 1899, 

 I pointed out that several electric and magnetic phenomena, especially 

 auroras and magnetic storms, might also be connected with the 

 pressure of radiation. C. T. R. Wilson found that the negative ions 

 condense vapours more easily than do positive ions. Without doubt the 

 gases in the atmosphere of the sun are practically ionised by the 

 ultra-violet radiation. Therefore we have to suppose, that among 

 the little drops formed by condensation in the sun's atmosphere far 

 more are negatively charged than are positively charged. As these 

 drops are driven away by the pressure of radiation they charge with 

 negative electricity the atmospheres of celestial bodies, e.g., the earth, 

 which they meet, till the charge is so great that discharges occur, and 

 cathode rays are formed, which carry the charge back to the universe. 



A calculation of the speed, with which these particles move through 

 space, will not be without interest. Suppose first, for simplicity, that 

 the pressure of radiation is double that of the weight of the particles 

 in the neighbourhood of the sun. It is not difficult to calculate, that 

 in this case the time, necessary for the particle's passage from the surface 

 of the sun to the earth, amounts to 68*7 hours. The specific weight is 

 supposed to be that of water. 



Now, after Schwarzschild's calculations, a perfectly reflecting drop 



