RADIOACTIVITY 



27 



definite portion of its range : the whole curve is lowered by 

 the same amount, as shown in fig. 9. The drop in different 

 parts is not quite the same but for present purposes this 

 variation is not worth consideration. Now this can only mean 

 that every a particle has gone through the screen without losing 

 its original direction of motion. If any had been lost in going 

 through, the curve would have shrunk sideways as in fig. 10; 

 the intensities of the various streams would have been dimin- 

 ished. There is no sign of this. If the particles had been much 

 scattered the curve would have lost its feature and become 



lorvisaYtorx. • 



Fig. 10. 



blurred and we might have got something of the form shown 

 in fig. 11. But the curve loses no detail, as is shown in fig. 9; 

 no conclusion seems possible other than that already stated. 



Every a particle therefore passes through the screen with 

 the same loss of energy and there is no appreciable deflection 

 of the particle from its original line of motion. Now the 

 particle is a projectile ; and it must therefore have kept to 

 the same line of motion all the way through the plate, for 

 it has no intelligence and it could not recover a line once 

 it had left it. It has therefore had no collisions to deflect it. 

 But its line of motion through the plate must have taken 



