189 l.J On the Pressure of Wind on Curved Vanes. 51 



Table showing the Relation between Resistance and Curvature. 



The negative sign placed before the versine means that the convex 

 surface is facing the wind. In each case the area of the plate is 



1 sq. ft. 



Area of B/elative pressure 



Chord. Versine. projection. per sq. ft. 



7-6 in. -3'8 in. 0'633 sq. ft. 72 



8-4 -3-6 0-70 72 



9-0 ,. -3-3 075 70 



10-8 -2-1 0-90 80 



11-6 -1-5 0-97 82 



12-0 1-00 114 



12-0 0-5 1-00 126 



11-8 1-0 0-98 129 



11-6 1-5 0-97 130 



10-9 2-0 0-91 127 



9-0 3-3 0-75 129 



The values could not be obtained beyond this on account of the 

 fluttering of the plate. 



The following values are given here for the sake of comparison. 

 They were obtained in May, 1889, by a similar method. The pres- 

 sures are expressed per sq. ft. in the same scale : 



A 9-in. Robinson cup, concave 132 



convex 45 



A 5-in. Robinson cup, concave 126 



,, convex 55 



A plate 6 in. diameter, with cone angle 90 at back . . 112 



The same with cone in front 74 



A plate 6 in. diameter, with cone angle 30 at back . . 115 



The same with cone in front 45 



From these values the curve given below showing the relation 

 between the pressure per unit area and the curvature has been con- 

 structed in a manner suggested by Professor Darwin. The ordinates 

 give the resistance per unit area of projection of plate, and the 

 abscissae the angle subtended by a section of the plate at the centre 

 of curvature. 



There are one or two points in the curve which call for special 

 notice. 



The scale of pressure is the same as in the other tables and 

 diagrams, and 100 in the scale represents a pressure of 1 Ib. per 

 sq. ft. at a velocity of 18^ miles per hour. It was originally chosen 

 so that 100 might denote the pressure upon a square plate of 



E 2 



