﻿Solution of Problems in Diffraction. 6*3 



In answer to Mr. Barber Starkey's question : I think it 

 probable that each shred, during its passage through the air 

 from the tree to the earth, was kept stiff and straight by 

 mutual electric repulsion between its own parts, and was 

 shot into the earth as an arrow might be in virtue of its 

 velocity before touching the earth. I scarcely think that 

 after it touched the earth there could have been enough of 

 electric attractive force to " suck it into the ground " much 

 farther than its own velocity and inertia took it. The velocity 

 which it acquired after leaving the tree was certainly given 

 to it initially by electric repulsion from the tree, due to large 

 difference of potential between the tree and the earth. During 

 its flight it must have been strongly electrified ; and must 

 have experienced therefore an oblique force, becoming nearly 

 perpendicular to the ground before it struck. It is quite 

 certain that each shred must have been strongly electrified 

 (whether vitreously or resinously we cannot say) at the instant 

 of its leaving the tree. K. 



1X« On the Solution of Problems in Diffraction by the Aid 

 of Contour Integration. By Henry DAVIBS, B.Sc, Tech- 

 nical Institute, Portsmouth *. 



TTHHE general problem of diffraction consists of finding 

 I solutions of the equation 



V*=« 2vnr w 



The solutions must remain finite throughout the space 

 considered and must satisfy certain specified boundary con- 

 ditions. 



This equation is modified when assumptions are made 

 concerning the light vector. 



Consider the case of a wedge of angle «, -and assume that 

 the electric force — taken as the light vector — is parallel to 

 the edge of the wedge. Assume also that Vae tt( . Then the 

 general equation reduces to 



provided the origin of co-ordinates is taken in the edge of 

 the wedge, the latter being assumed to occupy the space 

 a<6<2ir. 



The boundary conditions are that V shall vanish at = 

 and at = a, and shall become infinite at a point (/ . 6'). 

 * Communicated by the Physical Society : read June 8, 1906. 



