672 Prof. E. Rutherford on the 



the central charge, that the field due to the uniform dis- 

 tribution of negative electricit}' may be neglected. In 

 general, a simple calculation shows that for all deflexions 

 greater than a degree, we may without sensible error suppose 

 the deflexion due to the field of the central charge alone. 

 Possible single deviations due to the negative electricity, if 

 distributed in the form of corpuscles, are not taken into 

 account at this stage of the theory. It will be shown later 

 that its effect is in general small compared with that due to 

 the central field. 



Consider the passage of a positive electrified particle close 

 to the centre of an atom. Supposing that the velocity of 

 the particle is not appreciably changed by its passage through 

 the atom, the path of the particle under the influence of a 

 repulsive force varying inversely as the square of the distance 

 will be an hyperbola with the centre of the atom S as the 

 external focus. Suppose the particle to enter the atom in 

 the direction PO (fig. 1), and that the direction of motion 



on escaping the atom is OP'. OP and OP' make equal angles 

 with the line SA, where A is the apse of the hyperbola. 

 £> = SN = perpendicular distance from centre on direction of 

 initial motion of particle. 



