SOME CONTEMFOR.INV .tl>i:it\CF.S IX I'liysiCS 17// 421 



\oIis and so with a niiinliiT of oIIuts. I L;i\i' llii'sc and a fvw 

 other vahit's in the following lal)le: 



TAItl K 1 



It will he noticed that values are given for several excited states in 

 the same column; these rest upon evidence of the same sort as docs 

 the first e.xcited state, so that in general the atom must be cf)nsidered 

 to jxissess not one onl\', but se\eral possible states in addition to its 

 normal state. 



It will be noticed also that values are given for the "ionized atom." 

 These are the amounts of energy just sufficient (when applied by 

 means of an impinging electron) to detach an electron froin the atom. 

 When electrons with so much energy or more are poured into the 

 gas in question, positively-charged particles, such as I previously 

 mentioned and characterized as the residues of atoms deprived of an 

 electron apiece, appear in it. It is not absurd to call this an "excited 

 state." If it takes just 24.5 equivalent volts of energy to detach an 

 electron from a helium atom, then the system formed of an ionized 

 helium atoin and a free electron has a potential energy of 24.") equiva- 

 lent volts. Any experiment, therefore, in which the energ\' required 

 to detach an electron from an atom is measured — any experiment 

 for determining the ionizing- potential, as this energy when expressed 

 in equivalent volts is called — is essentially an experiment for locating 

 one of the excited states of the atom. 



In this sense the energ>'-values of the last line in Table I are to be 

 taken. I introduce them here for two reasons. In the first place, 

 the fact that this energy-value is greater than any of the others in 

 the same column suggests this interpretation f(jr the excited slates: 

 that they correspond each to a certain partial lifting-out of an electron, 

 to a certain stage of incomplete separation, while the energy-value of 

 the ionized atom corresponds to the total lifting-out or to the complete 

 separation. This idea is fortified by the fact that a helium atom 

 may be ionized by two consecutive blows from electrons each with 



