Appendix A. 



I append here the results of some additional experiments made with the Plane- Drop/ >< r 

 to determine the law of falling of a horizontal plane having a horizontal velocity of transla- 

 tion. It will be recalled that the preceding data given in the chapter on the Plane-Dropper 

 show only the total time of falling a distance of four feet, and that we cannot determine 

 from it the law of fall, unless we know, in addition, the relative diminution in the accelera- 

 tion during the descent, and whether at the end of the fall the plane has attained an 

 approximately constant velocity. For high horizontal velocities and for the most advan- 

 tageous planes, it is not impossible that an approximately constant velocity is reached within 

 the four-foot fall of the Plane-Dropper. In order to obtain these additional data, I placed 

 electric contacts upon the Plane-Dropper at intervals of every foot, and introduced other 

 modifications into the method of experiment. The accuracy with which it was necessarv 

 to measure the relative times of fall through successive feet precluded the further use of the 

 stationary chronograph for the registration, and I adapted a Konig chronoscope to this 

 purpose. 



This chronoscope consists of a tuning-fork of low pitch, which is made to vibrate by 

 the action of an electro-magnet. The vibrations are registered by a pen-point on a strip of 

 paper covered with lamp-black, which is passed over a roller during the time of fall. A 

 second pen-point worked by an electro-magnet records the passage of the falling-piece over 

 the five successive contact-pieces of the Plane-Dropper. On the same strip, therefore, we 

 have the relative intervals between the successive contacts, and a time-scale for their 

 evaluation. Although not essential for the evaluation of the intervals, approximate 

 uniformity in the motion of the strip of paper was obtained by fastening to the ends brass 

 clips differing suitably in weight, and converting this part of the apparatus into an Atwood's 

 machine. 



Two separate batteries were used, an electropoion battery of four cells, equivalent to 

 thirty or forty Daniel's cells, for vibrating the tuning-fork, and an ordinary battery of eight 

 cells for the Plane-Dropper and the quadrant contacts of the turn-table. The current from 

 this battery is forked into two branches, one branch running to the quadrant contacts of the 

 turn-table and to the observatory chronograph on which they register; the other branch, 

 going to the Plane-Dropper, actuates the release magnet, passes through the five electric 

 contacts, and thence goes to the electro-magnet on the Konig chronoscope, where these 

 contacts are registered, and finally back to the battery. This circuit is closed by a make- 

 key in the hands of the operator at the chronoscope. 



A preliminary calibration of the tuning-fork was made by connecting one pen of the 

 chronoscope with the mean time-clock, and obtaining a number of strips containing both 

 second intervals and tuning-fork vibrations. 



(109) 



