1890.] On Wind Pressure upon an Inclined Surface. 245 



x - 0-025 foot = 18 



x = 0-050 = 30 



x = 0-075 , = 45 



x = 0-100 60 



x = 0-125 = 70 



x = 0-150 6 = 75 



= 0-175 6= 78 



a; = 0-200 = 80 



Reverting to the whirling machine, the inconsistencies shown 

 between the series of results for the different positions appeared to 

 be due to an eddy from the frame of the apparatus, or at least that 

 seemed to me the only feasible explanation. To test this, experiments 

 were made on the machine with the plate MJN" in the position shown 

 in the annexed diagram, the wind being supposed to come from the 



right. If L be the moment about in this position, the expression 

 L sec 0, which is equal numerically to the force acting upon the 

 plate when exposed normally, ought to be independent of 0, but such 

 was not found to be the case. If a circle be taken with for centre, 

 and A be taken on the right, so that OA is the direction of motion of 

 the apparatus through the air, and the points F, B, be taken at 

 45, 90, and 135 respectively from A on the top, and H, C, G be 

 corresponding points on the bottom part of the circle, then the value 

 of L sec was found to vary in the following manner: 



At F the value was about 30 per cent, less than at E, the value 

 increasing uniformly from F to E. 



