Nipher — Method of Measuring Pressure on a Structure. 3 



was almost on the point of breaking into a deep musical note. 

 And still the pressure within the building was increased by 

 every increase in wind velocity. Within the building the 

 barometer measures the air pressure, modified by these wind 

 effects. 



If however we take the barometer outside of the building, 

 where it is exposed to the wind, it fails to measure the true 

 pressure of the air. The barometer is then an obstacle in the 

 wind. Some of the small openings leading into its air-spaces 

 may collect pressure from compressed air on the windward 

 side, and some from the rarefied air on the leeward side. In 

 addition the air sweeping across the mouths of such openings 

 produces rarefactions within, by an action which is utilized 

 in the atomizer. The barometer will then record the result- 

 ing air-pressure within its air spaces, just as inside the build- 

 ing it measures the air-pressure in the building. But this 

 gives no indication of what the pressure is outside of the 

 barometer. If we shield the barometer from the wind by 

 inclosing it in a box or casing, then we have simply placed it 

 in another house. The air-spaces of the box are then in the 

 uncertain condition which existed before in the barometer. 



The device which is to be used for measuring the pressure 

 at any point on a building, must consist of a collector, to be 

 placed at the point, and an indicator or gauge, to be placed at 

 any point where convenience demands, and a tube for trans- 

 mitting the pressure from collector to gauge. 



The collector must be small and portable. It must be un- 

 affected by the wind, but must collect and transmit changes 

 in pressure due to wind. Compressions and rarefactions due 

 to the collector itself, must not be allowed to affect the gauge. 

 The suction or atomizer action of wind blowing across the end 

 of a tube must also be prevented. 



After many failures the collector shown in Fig. 1 was 

 devised, and seems entirely satisfactory. The tube leading 

 from the pressure gauge, and shown in longitudinal section, 

 pierces a thin circular disk, having a diameter of 2^ inches. 

 The end of the tube is flush with the face of the disk. The 

 disk is ground to a thin knife edge as shown. A second 

 disk of the same size is screwed down upon the former. 



