the PLANK-i)i;orri:i;. 



r, 



planes is obtained only above a certain minimum velocity of translation. For 

 the present planes, of size 15x4 inches set 4 inches apart, this minimum velocity 

 is shown by the curves to be higher than <*>.•"> and less than 23.5 meters per 

 second, and, from comparison of all the data, apparently lies at about L3 meters 

 per second. These results substantially confirm those obtained from the experi- 

 ments of June 14, with this additional information as to the minimum velocity 

 at which the maximum sustaining power can be obtained for a distance apart 

 of 4 inches. For a distance of 2 inches apart even the highest velocities show a 

 serious diminution of efficiency. 



The results of these observations with two sets of planes, one above the 

 other, give us a first conception of the form and initial vertical amplitude of the 

 wave that is set in motion in the air by a plane passing horizontally through it 

 in the manner of these planes. 



Fie. G. 



Times of falling 4 feet of single and double pairs of 15 x 4 inch planes set at, different angles of 



elevation and having a horizontal velocity of 6.5 meters per second. 

 Abscissa? : = Angles of inclination of plane to horizon. 

 Ordinates : = Time of fall in seconds. 



These later observations also incidentally furnish additional data as to the 

 velocity of soaring. When inclined at an angle of 10° the single planes and 

 the double planes, at a distance of 4 inches apart and upward, are sustained in 

 the air if they have a horizontal velocity of about 13.2 meters per second. 

 When set at 1°, soaring took place at velocities from 21 to 23 meters per second, 

 ('lose observation also indicated that the error of vertically of the plane-dropper 

 during motion did not exceed 1° ; hence for these velocities the soaring angle 

 may be taken at about 2°. This is a fraction of a degree less than that given by 

 the observations of June 14, as plotted on Fig 3. 



The most general and perhaps the most important conclusion to be drawn from 

 them appears to be that the air is sensibly disturbed under the advancing plane 



