568 Sir E. Rutherford on Collision of 



Thus, 



X 10 n 1 

 u—-r i = ,__x .. r , =2*71 x 10° cm. per sec. 

 14 "155 2ob r 



The maximum \alue 



m = i- x 2'7Lxl0 9 =:ai2xl0 9 cm. per sec. 



o ( 



The calculated value o£ v =l'6 x 192 x 10 9 



= 3*07 x 10 9 cm. per second. 



The experimental and calculated values agree well within 

 the probable error of experiments. From the magnetic 

 deflexion we found that 



5°=3\L5xl0 5 , 



e 

 and from the electric deflexion 



. 7^ = 3-12 xlO 9 , 

 consequently, ejm = 10 i e.m. units. 



The value of e\m for the hydrogen atom in the electrolysis 

 of water is 9570. The agreement is sufficiently close to show 

 that the long-range scintillations produced by a particles in 

 hydrogen are due to hydrogen atoms carrying a unit positive 

 charge. The agreement between the calculated and observed 

 velocities shows that, within the margin of experimental error, 

 the conservation of momentum and energy hold for close 

 collisions between the atomic nuclei and that there is no 

 sensible loss of energy due to radiation. 



Brightness of scintillations. 



The maximum energy communicated to an H atom is '64 

 of the energy of the colliding a. particle. After passing- 

 through 12 cm. of air, for example, the energy of the H atom 

 is reduced to '44 of the energy of the particle. Supposing 

 that the H atoms are produced by a particles of radium C of 

 range 7 cm., the energy of the H atom after passing through 

 12 cm. of air, corresponds to an a particle of range about 

 2 cm. In practice, the brightness of the corresponding H 

 scintillations is much less than is to be expected from its 

 energy, and is not greater than that produced by an a 

 particle of range 5 mm. This relative lack of brightness of 

 H scintillations compared with a. particles of corresponding 

 energy holds for all velocities of the H atoms. Since we 

 have seen that we can rely on the calculations of the energy 

 of the H atom, it seems clear that the H atom is less effective 



