230 Mr Sharpe, Liquid Motion from a Single Source 
Figs. 4 and 5, in which OE — pirate accurately, OS = girajc 
accurately, and from (19) OB = ga/c to a first approximation, the 
second approximation being given by 
0j? = ^ + ( M + 6 _) ^a (26) 
c c 
Now suppose we keep g, c and a constant but increase b, 
we see from (26) that OB is increased, and from (18) that 
is decreased, and because b has been increased, by Art. 4 the 
reflecting power of the boundary has been increased. In Fig. 5 
therefore the velocity at a distance is greater than in Fig. 4. 
This is exactly analogous to a remark made by Lord Rayleigh in 
his Sound, Art. 280, where in treating of conical pipes with a 
source of sound at the vertex of the cone, he says that when the 
angle of the cone is decreased the intensity is increased. It will 
be noticed in Fig. 5 that the boundary is more cramped in the 
neighbourhood of the source than in Fig. 4. See also Sound , 
