288 MODERN SCIENCE READER 



matter or new substance. These are pitched away with 

 extraordinary violence as the atom breaks up ; they produce 

 by their bombardment of zinc sulphide the bright little 

 flashes seen in Crookes' spinthariscope, and they likewise 

 generate heat when they are stopped by any obstacle. They 

 thus keep the vessel in which they are inclosed at a tempera- 

 ture a degree or two above surrounding bodies, at least in 

 the case of the most active known substances, radium and 

 its emanation. For radium converts its own intra-atomic 

 energy into heat at so surprising a rate that it could, if all 

 of the heat were economized and none allowed to escape, 

 raise its own weight of water from ordinary temperature 

 to the boiling-point every hour. 



The number of atoms breaking up in any perceptible 

 portion of radium salt must be reckoned in millions per 

 second; nevertheless, the proportion of atoms which are 

 thus undergoing transformation at any one time is ex- 

 tremely small. If they could be seen individually most of 

 them would appear quiescent and stable. Of every ten 

 thousand atoms, if a single one breaks up and flings away 

 a portion of itself once a year, that would be enough to 

 account for all the activity observed, even in the case of 

 so exceptionally active a substance as radium; hence the 

 apparent stability of ordinary matter is not surprising. 



The thus projected atomic fragments were measured by 

 Rutherford, who found them deflected by a magnet in the 

 opposite direction to the electron projectiles, and were 

 therefore proved to be positively charged; but they are 

 deflected so slightly that they must be very massive bodies, 

 1,600 times as massive as an electron, or twice the weight 

 of hydrogen. A substance with this atomic w r eight is 

 known, viz., helium: and surely enough the discoverer of 

 helium, Sir W. Ramsay, working with Mr. Soddy, a recent 

 colleague of Rutherford, has witnessed the helium spectrum 

 gradually develop in a tube into which nothing but radium 

 emanation had been put. 



Matter, then, appears to be composed of positive and 



