THE PLANE-DROPrER. 



29 



when the whirling table is in motion, which appear in the observations. The 

 probable error ot* the measured time of falling in still air, when only instrumental 

 errors are present, is within T l s of a second. 



The first series of experiments with horizontal planes was made May 25 

 and June 10 to June 14, 1S89, and was devoted to the first two objects already 

 set forth, namely : 



1st. To show by the increased time of fall that the supporting power of the 

 air increases with the horizontal velocity cf the body; and, 



2d. To get first approximations to the times of falling of rectangular planes of 

 different shapes and aspects, the latter condition having reference to whether the 

 long or the short side of the rectangle is perpendicular to the direction of advance. 



An abstract of the note book for June 11, 1889, is given here as an example 

 of the detailed records made in these experiments. 



June 11, 1889. — S. P. Laxgley, Conducting experiments and recording; F. W. Very, Assisting. 



Notes : "A" and " B " designate the direct and reversed positions of the brass frame and falling 

 piece ; belt on third pulley. 



To determine time of falling. 



The detailed observations with the five different planes already described 

 are contained in Tables VI and VII, and the results are presented graphically 

 in figure 2, where the times of fall are plotted as ordinates, and abscissa3 are 

 horizontal velocities of translation. 



