1884.] Determination of Pressures of Granular Substances. 229 



were employed in weighing the side pressures, and the slide for 

 admitting and stopping the grain between the weighing-machine and 

 the bin was similar to that described for bottom pressure, only that 

 it ran on edge instead of horizontally. The details are shown on 

 the figure. 



The method adopted in weighing both the vertical and lateral 

 pressures was the following : On three sides of the bin, painted gauge 

 boards were affixed and marked in feet, and each foot was subdivided 

 into spaces of 3 inches. These boards extended from the top of the 

 weighing-machines to the top of the bin, and tne quantity of grain 

 which I desired to weigh was put into the bin and carefully levelled at 

 the desired height, by the aid of these marks. Then three or more 

 weighings were taken at that level. Afterwards the height of the 

 grain in the bin was increased to the next desired stage, and then 

 levelled and weighed three times, or more, and so on, stage by stage, 

 until the bin was filled. 



Before the grain was allowed to come in contact with the weighing- 

 machines, care was taken always to place an excess of weight upon 

 the levers, and this was reduced to indicate the pressure by moving 

 the sliding weight by means of the cord along the graduated edge of 

 the lever. The reduction of the weight on the weighing-machine 

 was therefore steady and gradual. 



I had not proceeded far with the process of weighing, when I 

 observed a constantly recurring stiffness in the rising of the levers off 

 their rests. They would rise, say one-fiftieth of an inch off the rest, 

 and there remain for an indefinite length of time without the least 

 further movement ; but as 1 lb. weight after another was removed off 

 the lever, it gradually rose until the balance was finally overcome, 

 when the lever would rise and touch the check which prevented 

 further motion upwards. The difference between the first movement 

 and the final rise of the lever frequently equalled one-half the whole 

 pressure. This condition invariably accompanied every weighing. 

 The machines were carefully examined, but no fault lay there, and 

 I infer that the difference here referred to represents the elastic force 

 of grain when it is subject to pressure, and that this elastic force 

 expends itself before the mass of the grain comes into the state of 

 mobility. 



In the following tables, which contain the results of each reliable 

 weighing which was made, I distinguish between the first small move- 

 ment of the lever and the final movement which represents the grain 

 in motion, by the words Dormant and Active pressures. I call the 

 pressure dormant when the lever has been lifted off its rest to the 

 extent that a beam of light can be seen between the lever and its 

 rest ; and the pressure active, when the lever has risen about three- 

 fourths of an inch above its rest up to the check. 



