Nipher — Method of Measuring Pressure on a Structure. 5 



out through a stopper, and was taken to the air space in a 

 cistern half full of water. The capacity of the cistern was 

 about 100 cubic centimeters. From the bottom of the cistern, 

 a glass tube one meter long, and having an inclination of 5 in 

 100, served as a gauge for indicating air pressures in the 

 cistern. A second tube entered the stopper of the bell-jar. 

 The effect of breathing gently into the mouth of this tube, 

 and producing a slight compression of the air in the bell-jar, 

 is instantly seen in a rise in the water column of the gauge. 



In order to test the collector in a high wind the apparatus 

 was taken upon a passenger car. The water gauge was 

 clamped to a window sill. The doors were opened at each 

 end of the car. The ventilators and windows were also 

 opened, so that there was a free circulation of air through 

 the car. There was no appreciable atomizer action on the 

 gauge. The collector was thrust out of the window, and 

 held edgewise in the wind at a distance of thirty inches from 

 the side of the car. The connection between collector and 

 gauge was then made and broken. No effect was produced 

 on the gauge. This experiment has been repeated at various 

 times, and in one case when the train traveled between two 

 stations fifteen miles apart in fifteen minutes by the watch. 

 When the hand is placed tangent to the windward or leeward 

 edge of the collector, the gauge at once shows a marked 

 decrease or increase in pressure. The wind in free air does 

 not affect the gauge, but any change in pressure is at once in- 

 dicated. It was also found that the collector might be held 

 in any other position in the wind, with no appreciable change 

 in the result.* The wire layer was cut off even with the edge 

 of the metal disks. When placed edgewise in the wind, a 

 marked increase in pressure was then shown. When turned 

 7-^° around a diameter at right angles to the lines of flow, this 

 increase in pressure disappeared. For greater angles the 

 gauge showed an exhaust. 



The disk collector thus appeared to satisfy all of the re- 

 quirements, and justified more serious attempts to test its 

 limitations. 



* This has only been tried with the fine brass wire, but with from two 

 to twelve thicknesses. 



