1884.] Determination of Pressures of Granular Substances. 23& 



aperture of 9 square feet with the head or height of 49 ft. 6 ins. 

 of peas to be 1391 lbs., and with the head of 9 ft. the pressure of 

 1323 lbs. With the bottom aperture of 4 square feet (Table VIII) 

 and the head of 49 ft. 10 ins., the maximum dormant pressure of 

 726 lbs. was indicated, and with the head or height of 6 ft., 723 lbs. 

 The apex of the pressure paraboloid is therefore at the height of three 

 diameters of the inscribed circle of the base or aperture, and is greater 

 by one diameter than the wheat paraboloid. The constant (c) for 

 peas is, in the case of the 9 ft. aperture, 0*96 ; the corresponding 

 constant for wheat being 0'84. 



The lateral pressures are given in Tables IX and X, where, with 

 the aperture of 9 square feet and a head of 43 ft. 10 ins. of peas, the 

 maximum dormant pressure was 242 lbs., and with the head of 9 ft. 

 251 lbs. With the aperture of 4 square feet and head of 43 ft. 9 ins. 

 the maximum dormant pressure was 121 lbs., and with a head of 6 ft. 

 97 lbs. It therefore appears that all lateral pressure ceases at a 

 height equal to three times the breadth of the aperture as indicated 

 by the 9 ft., and that the pressure is slightly greater as indicated by 

 the 4 ft. square aperture. 



With the 9 ft. it is 27*89 lbs. on each square foot, and with the 

 4 ft. it is 30*25 lbs. The pressures of wheat corresponding with these 

 (Tables IV and V) were 42*78 lbs. and 59*5 respectively. 



The conclusions to be drawn are, that the vertical or bottom pres- 

 sure of peas is greater than that of wheat in the ratio of 0'96 to 0'84, 

 or of 1*73 to 1*66; but that the lateral or side pressure of peas is 

 less than that of wheat in the ratio of 27*89 to 42*78, or of 30*25 to 

 59*5. 



The constant (c = 0*96) for computing the vertical pressure is safe 

 for the equilibrium of peas, wheat, or any other grain, but the safe 

 permanent sustaining powers of any floors or walls should be at least 

 four times the constant. 



For the lateral pressure, 50 lbs. upon each square foot of retaining 

 wall is safe for the equilibrium of all grain ; but the safe permanent 

 resistance to pressure in any wall or partition should not be less than 

 four times that, or 200 lbs. upon each foot. 



It will have been observed that the maximum dormant pressure has 

 been adopted in the formulas for both the vertical and lateral pres- 

 sures, though the active pressure is that which would cause the 

 breaking down of the structure, and, as shown in the tables, it is 

 considerably less than the dormant. 



Seeing that the constants for the vertical pressures of both wheat 

 and peas are so near unity, one being 0*84 and the other 0*96, I 

 propose to adopt unity in the formula, which will then stand finally 

 thus : — 



a x dxw=jp, 



