PROCEEDINGS OF THE OHIO ACADEMY OF SCIENCE. 337 



radiation, the alpha-rays, which are positively charged particles 

 of atomic size, the beta-rays, which are negatively charged par- 

 ticles many times smaller than an atom, — probably free elec- 

 trons, like the cathode-ray particles, — • and the gamma-rays, 

 which are apparently short ether-waves similar to the X-rays, 

 and very probably are disturbances set up by the impact of the 

 beta-rays on some part of the radio-active body itself. The energy 

 developed during these radio-active changes by a given mass of 

 radium is very considerable, enough to melt its own weight of 

 ice in an hour, and to keep its temperature permanently above 

 that of the surrounding objects by an amount dependent on the 

 circumstances, but often as much as two or more centigrade 

 degrees. It seems probable that a large mass of radium, a kilo- 

 gram or so, would be permanently red-hot. 



Besides these three forms of radiation, all radio-active 

 bodies give otT in small quantities substances which are them- 

 selves radio-active, but which after a longer or shorter time lose 

 their active properties. The substance given ofT by radium was 

 called by Rutherford radium emanation. It was itself radio- 

 active, had a characteristic spectrum, and in other respects mani- 

 fested all the properties of a gas of high molecular weight, 

 chemically similar to the group of inert gases, to which helium 

 and argon belong. It loses 99 per cent of its radio-active power, 

 and practically disappears, or is transformed into something else, 

 in about a month. Ramsay and Soddy showed that the spectrum 

 of this gas, altering from day to day as the gas altered or de- 

 cayed, became finally the well-known spectrum of the rare gas 

 helium. It cannot be inferred from this, however, that the 

 emanation had turned into helium. Rutherford showed definitely 

 in 1909 that alpha-particles from whatever source, when freed 

 from their positive charges, become simply atoms of helium. The 

 emanation is in all probability an elementary substance (in the 

 ordinary chemical use of that word), though a short lived one, 

 and may be regarded as the residue left when an atom of radium 

 has emitted an alpha particle. The emanation in like manner 

 emits from each atom an alpha particle, changing thereby into 



