THE RESULTANT PRESSURE RECORDER. 



17 



greater pressure. Preliminary experiments were therefore made witliout tlie wind 

 plane for detecting this effect, with the result that no sensible difference was 

 apparent between the pressure on the inner and outer arm, even at the highest 

 speeds. 



On August 25, 1888, the spiral springs were calibrated by hanging weights 

 of 1, 2, and 3 pounds to the center of the springs and marking the displaced 

 position of the center when the system was rotated through successive octants in 

 the manner already described. Experimental circles were drawn through the 

 system of points, and, the departures of the individual points being very small, 

 the cii-cles were adopted as the curves giving the relation between pencil excursions 

 and pressures. From these curves the following table has been constructed : 



Table I. 



After many days of preliminary experimentation, in which the instrument 

 was o-radually perfected by trial in successive forms before being brought to the 

 condition to which the foregoing description applies, two days' experiments were 

 made on August 27 and 28, and a final series on October -1, 1888. These 

 are presented in detail in tlic accompanying tables, and consist of sixty-four 

 separate experiments made with the plane set vertical and at angles varying 

 between 5° and 45° with the horizon. The mean temperature is obtained from 

 thermometer readings at the beginning and end of each set of experiments, which 

 usually continued from one to two hours. The mean wind velocity is obtained 

 from the readings of a Casella air meter. The apparatus is so placed upon the 

 whirliuff arm that the center of the wind plane is nine meters from the axis of 

 rotation. One registering sheet serves for a group of observations, consisting in 



3 



