Nipher — On Pressure Measurements in a Fluid Stream. 19 



described and figured has been found effective for wind pres- 

 sure work. (pp. 4 and 9). For eliminating velocity effects 

 in small pipes through which air is being forced, it is desira- 

 ble to make the disk small. The leading in tube may also be 

 small, since the pressure is in such cases much more nearly 

 constant, than is the case in wind pressures against buildings. 

 In such cases it is better to place two circular disks of wire 

 cloth on each side of the disk, so that the collector shown in 

 the former paper is sandwiched between them. The arrange- 

 ment is then as shown in Fig. 1. The collector is now made 

 in this way for all purposes. 







Fiii. 1. 



It is evident thai in measuring wind velocities above the 

 top of a building, by means of a Pitot tube collector attached 

 to the wind-vane, the open end of the water gauge to which 

 the Pitot tube leads, must not be exposed to the stream 

 of air which is being measured, nor must it communicate 

 with the air within the building around which the wind 

 sweeps. It must be connected with a disk-collector (Fig. 1) 

 placed far above the building, and standing edgewise in the 

 wind. The plane of the disk is to be horizontal. 



These complications caused the writer to seek some 

 method of verifying Newton's equation in which the Pitot 

 tube itself was moved through the air. One such method 

 has been described in a former paper.* That method in- 

 volved the exposure of the tube from the window of a rail- 

 way car, having its windows opened. 



* Trans. Acad, of Sc. of St. Louis. X: 215-227. 



