Nipher — Method of Measuring Pressure on a Structure. 23 



But it is very desirable to determine what these, pressures 

 really are. 



The observations on pressures should be supplemented with 

 simultaneous observations on wind directions. A vane with 

 a cup collector connected with a gauge below will determine 

 pressure, due to the free wind, from which velocity may be 

 computed. 



Two metal brushes 180° apart are attached to two insulated 

 rings surrounding the vane-tube. The poles of a* battery 

 connect with these rings by sliding contact. A flat commu- 

 tator with 72 segments surrounds the tube and the two 

 brushes slide upon it, touching opposite segments. The 

 wires lead in a cable to the closed copper windings on an iron 

 ring at the pressure gauges. The wires of the cable connect 

 to these windings at equidistant points, those coming from 

 opposite commutator bar3 leading to opposite points in the 

 winding, and adjacent wires at the commutator being adjacent 

 at the ring. The arrangement is exactly that of the Gramme 

 armature. The polarity of the ring will follow the shifting 

 of the vane. A magnetic needle whose pivot is at the center 

 of the ring will follow the vane. This needle may be photo- 

 graphed with the scales. With comparatively small expense 

 it will be easy to obtain information of great value, even with 

 ordinary winds. At some of the mountain observatories, 

 destructive winds are not uncommon, and it is desirable that 

 such work should be undertaken there. In conclusion I wish 

 to express my grateful thanks to Professor Timmerman and 

 Mr. Schlossstein for their enthusiastic aid under circumstances 

 which were very far from inviting to one seeking rest and 

 quiet. My thanks are also due to Mr. Stuyvesant Fish and 

 Mr. A. W. Sullivan, President and General Superintendent 

 of the Illinois Central Railroad, through whose co-operation 

 we were enabled to do the work, and to Mr. Joseph Boyer for 

 the loan of his Speed Recorder. There are dozens of others 

 who have assisted us greatly in various ways, whom I cannot 

 name. The names of some of them I do not even know. 

 But it was a constant pleasure to receive their aid, and I feel 

 that much of the success we may have attained was due to 

 such friendly assistance. 



