APPENDIX A. 



Ill 



The first contact i.s not at absolute rest, but a fraction (0.4 or 0.5) of an inch below the 

 position of rest ; hence, when it records, the plane has already attained a small velocity. 

 To this is due the fact that the time of falling the first foot, which is registered by the first 

 and second contacts, is less than the computed time in vacuo by .03 second. At least this 

 amount should therefore be added to the observed time for the first foot, and the total time 

 will be 0.53 seconds. This gives a total retardation of 0.03 seconds, due to the resistance of 

 the air. Attention is called to the symmetrical character of the diflerences between the 

 observed and the computed time in vacuo, showing the increasing retardation corresponding 

 to increasing velocities of fall. Being assured by these results of the perfect adaptation of 

 the apparatus to secure the desired data, the Plane-Dropper was placed upon the whirling- 

 table December 13, 1890. 



When the whirling-table has attained uniform motion at the speed desired, a signal is 

 given to the observer seated at the Konig chronoscope to proceed with the experiment. 

 First, by a break-key he cuts out for a moment the quadrant contacts as an evidence on 

 the chronograph sheet of the time of the expei'iment. Second, the chronoscope strip, which 

 has previously been prepared and placed upon the roller, is set in motion by the release of 

 a detent, and an instant later, when the strip has gotten fully into motion, the make-key of 

 the Plane-Dropper circuit is pressed, relea.sing the falling plane. As the falling plane passes 

 each of the five contact pieces the circuit is completed, and registration is made upon the 

 Konig strip. In two seconds after setting in motion the Konig strip the experiment is at 

 an end. The strip containing the record is then passed through the solution of shellac and 

 alcohol for setting the trace, after which it is measured at leisure. Meanwhile a new strip 

 is placed upon the chronoscope, and the apparatus is in readiness for another trial. 



The results of the observations covering a range of horizontal velocity from G to 26 

 meters per second (13.5 to 58.5 miles per hour) are contained in the accompanying table. 



To find llie times of falling successive feet of planes haoing a Iiorizontal velocity. 



December 13, 1890. 



F. AV. Very, G. E. Curtis, Observers. 



One pair 12x6 inch planes horizontal ; weight, 464 gi-ammes (1.02 Ihs.) ; mean temperature, 0° C. ; wind 

 velocity, l.So meters per second. 



TIMES OF FALL AT DIFFERENT HORIZONTAL VELOCITIES. 



* Seriously affected by wind. 



