244 Mr. W. H. Dines. [June 19, 



FIG. 7 . 



shown in figs. 6 and 7 was designed. A pressure plate, P, similar to 

 the experimental plate, was mounted on a steel rod, AB, the line of 

 the rod being on the face of the plate, and parallel to a vertical edge, 

 but not necessarily passing through the centre of the plate. The rod 

 was ground to a sharp point at its lower end and placed in a piece of 

 brass tube with a plug at the bottom, on which the point rested, so 

 that it could turn freely in the tube. On exposing this arrangement 

 to the wind the plate could take up a definite position, the angle 

 between the normal and the wind direction being dependent upon 

 the distance of the centre of the plate from the axis of rotation formed 

 by the steel rod. 



It was not possible, however, to measure this angle, because the 

 wind direction never remained steady for a sufficient time. To over- 

 come this difficulty, a flat disc, C, was placed on top of the brass tube, 

 and the tube itself was pivoted in another piece of tube. A definite 

 line on the disc was kept facing the wind by a vane D, and the angle 

 between the normal to the plate and this line was determined, as far 

 as possible, for various positions of the steel rod relatively to the 

 centre of the plate. A vertical section is shown in fig. 6 and a plan 

 in fig. 7. In the following table the angle of incidence is denoted by 

 6, and the distance between the centre of the plate and centre of 

 pressure by x. Exact relations between x and 9 could not be obtained, 

 but the following values are probably within a few degrees of the 

 truth, unless the wind vane below the disc is influenced by the 

 pressure plate. Whether this be so or not I have no means of 

 judging. 



