238 



Mr. W. H. Dines. 



[June 19, 



to the first entry, gave the distance from the axis at which a weight 

 of 2 Ibs. would cause equilibrium. 



The change of the plane of the couple from the vertical to the 

 horizontal was also accompanied by a change in the length of the 

 arm of the couple in the ratio of 2:1, the apparatus being designed 

 thus in order to reduce the weight of the sliding bar ; and therefore 

 the value of x, when found as above, had to be multiplied by 4, to give 

 the distance in feet at which the centrifugal force acting upon 1 Ib. 

 would balance the pressure upon the plate. 



In the event of the small bar having run against its stops at either 

 end, a fresh adjustment of the heavy bar had to be made by hand ; 

 but this seldom happened, except in the case of the first determina- 

 tion for a new position. 



Position I. 



Position II. 



Position III. 



Position IV. 



The four typical positions are shown in the figures, and are referred 

 to in the subsequent tables and remarks as Positions I, II, III, and 

 IV. The following extract, taken from Professor Darwin's memo- 

 randum, shows how the normal component of the wind pressure and 

 the position of the centre of pressure may be obtained : 



" It may be supposed that the couple, due to the wind pressure 

 upon all the moving parts except the plate, may be eliminated, so 



