comp:ts^ tails, hie corona, and the aurora 



150REALIS." 



By Prof. John Cox, 



Mr a ill Uiiin-rxili/. 



There is und('iiia1)le fascination a1>out a th(M)r\' wiiicli includes within 

 its sweep the time-honored problems of astrononi}' connected with 

 comets' tails and the reason why the}' point awa}^ from the sun; the 

 solar prominences and the corona; the source of th(^ lig-ht hy which 

 the nebula' shine; the origin and structure of meteor swarms; and the 

 aurora borealis; besides solving incidentall.v half a dozen minor out- 

 standing mysteries of the heavens. 



Such a theory has been ad\'anced by Sweden's distinguished chemist 

 and phj'sicist, Svante Arrhenius, in a paper pul)lished in the Physi- 

 kalische Zeitschrift for November, l!»0(). Its main points were brietly 

 mentioned with appro\'al by no fess an authority than Prof. J. J. 

 Thomson at the end of his captivating article on "'Bodies smaller than 

 atoms" in the August number of the Popular Science ^Monthly. All 

 the physical principles on which Arrhenius relies, with one exception, 

 are explained at length in that article, and are now very generally 

 accepted. We may therefore say that the theory is based on *'vene 

 causi\?,'' and its accordance with known facts is so impressive when 

 the comparison is made in detail that I venture to think the readers 

 of Professor Thomson's article will ])e interested in a more complete 

 statement of Arrhenius's views than time permitted him to give. 



Let us begin by taking stock of the physical principles already to 

 hand. We know (Professor Thomson's paper) that corpuscles, about 

 1,000 times smaller than hydrogen atoms, and each l)earing a chai'ge 

 of negati\ e electi'icity, are discharged with high velocity: 



(1) From the negative electrode in a Crookes tube (catiiode rays). 



(2) From hot ))odies, such as glowing nu'tals. 



(3) From cold metals under the iuHuence of ultra-\iolet light. 



(4) From the radio-active substanc(^ radium. 



Again we know that these corpuscles, or ions, in passing through a 

 ga> produce other ions by collision with the molecules of the gas, and 

 that the negatively charged ions are capable of ser\'ing as nuclei for 

 the condensation of ordinary matter. 



« Revised by the author from article in Po})nlar Science Monthly, January, 1902. 



17!) 



