266 C. E. BUTTON 



of ionization, greatly exceeding the open atmosphere and the air in 

 closed vessels. This is attributable only to the presence of radium 

 emanation diffused from surrounding rocks or soils. Many common 

 well waters give satisfactory tests of the presence of radium emana- 

 tion, which is soluble in water — more so than most gases. 



The most pronounced occurrence of radium is in hot springs. Their 

 waters always give evidence of its presence, and sometimes in quanti- 

 ties many times exceeding the air taken from the soil or cellars. Hon. 

 R. J. Strutt, of Trinity College, has devoted much attention to the 

 Springs of Bath, and finds not only radium emanation in their waters, 

 but actual radium in the deposits of the springs. The hot springs of 

 Baden Baden have been found to contain radium salts. M. Curie has 

 tested a large number of the mineral springs of central and southern 

 France, and finds radium emanation in nearly all of them. Mr. 

 Boltwood, of New Haven, has devoted considerable attention to the 

 study of radioactivity in mineral springs, and finds that many of the 

 waters of America contain radium emanation. 



It does not appear that any extensive or systematic investigation of 

 the emanations of active volcanoes and volcanic gases has been 

 made. The only one I can discover is the observation of Rausch von 

 Trauenburg on the crater of Vesuvius. The gases from that orifice 

 produced marked ionization and a prompt discharge of the leaves of 

 the electroscope. The subject, however, needs thorough investigation 

 at many other volcanic vents. 



The general result of the investigation, so far as it has gone, has 

 been to make clear the fact that the amount of radioactivity in the 

 earth much exceeds the amount which is necessary, so far as the 

 heat generated by it is concerned, to compensate the loss of heat by 

 conduction and radiation. In fact, it appears that the thermal condi- 

 tion at present is one of continual increase of internal temperature of a 

 large portion of the earth, or is so in part, or else is one of equilibrium 

 between loss and gain. Undoubtedly the amount of radioaction varies 

 somewhat widely in different portions of the earth's interior, in 

 some portions permitting a loss of heat, in others permitting a gain. 

 And when there is a gain, it may proceed in the portions near the sur- 

 face so far as to liquefy the rocks, and thus furnish all the conditions 

 necessary to volcanic eruptions. 



