132 



Mr. Willis on the Pressure of a 



weights are required to pull it off, till we reach a certain point 

 beyond which the same or a rather less weight is required, how- 

 ever the diameter of the disc be increased. Also that the weights 

 increase with the increase of the orifice, or of the pressure. 



TABLE II. 



TABLE III. 



To understand these phenomena more perfectly, it is necessary 

 to have some means of estimating the pressure on the lower surface 

 of the disc at any required distance from its center. I shall pro- 

 ceed, therefore, to describe an insti'ument which is adapted to 

 this purpose. 



Fig. 2, a section. 



Fig. 3. Plan of the lower surface of FG seen from below. 



ABCD is the lower plate having a tube B opening at its 

 center, and communicating with the wind-chest. 



