I9I4] 



ATMOSPHERIC PRESSURE. 



61 



wind speed of the test wire in cm. per sec. was taken as 2tz X cm. 

 fork radius X speed of motor in r.p.s. At the other end of the 

 motor-shaft was coupled a small magneto-generator for indicating, 

 by its e.m.f., the speed of rotation. The fork-motor-magneto 

 mechanism is illustrated in Fig. 4, supported on a wooden frame 

 intended to be held in place inside the pressure tank, which is shown 

 with the manhole open. 



Fig. 4. Photograph of Fork, Driving-Motor, Magneto Speed-Indicator and 



Pressure Tank. 



Pressure Tank. 



The pressure tank in which the motor and fork were supported 



was a vertical steel cylinder of Yt." (1.25 cm.) steel plates, riveted. 



Figure 5 shows the dimensions of the tank, and also the position 



within it occupied by the motor and fork. The radius of the fork 



