380 
PROFESSOR H. S. HELE SHAW ON THE THEORY OF 
distribution of all the rollers being shown by figs. 13 and 14 (p. 17), which are 
respectively a diagrammatic plan and elevation of the arrangement. In fig. 11 the 
movable frame is for the sake of clearness omitted, but it is shown in plan in fig. 12. 
Figs. 9 and 10. 
The principle upon which the area of any curve is integrated when the pointer has 
passed round the periphery is perfectly simple. In fig. 15 (p. 383) let ON, the axis 
of x, be the trace of roller A on the cylinder, let P be the position of the pointer at 
any point on the curve for which the ordinate 
PP'=y 
PN =y 2 
P'N=y 1 
The motion of the roller B when the pointer passes along the line hPg gives in 
suitable units 
= area of curve hVglm. 
