Appendix C. 



At the time of my experiments to determine the varying position of the center of 

 pressure on an inclined plane moving in the air, I was unacquainted with the similar 

 experimental work of Joessel* and of Kummerf in the same field. Joessel, who appears 

 to be the first experimenter on the sul)ject, found for a square plane of length L that, as 

 the angle between the plane and the current is diminished, the center of i^ressure approaches 

 a point i L from the forward edge, and that its position for any angle « between the plane 

 and the current may be represented by the formula 



d = (0.3 — 0.3 sin a) L, 



d being the distance of the center of pressure from the center of plane. 



The method of experiment adopted by Ivummer is essentially similar to the one pur- 

 sued by me in the use of the Counterpoised Eccentric Plane. Tlie object is to determine the 

 position of the center of pressure corresponding to different angles of inclination of a plane 

 to the current. The method pursued both by Kummer and myself has been the one which 

 most naturally suggests itself to find the angle of inclination a of the plane corresponding 

 to a series of fixed distances d of tlie center of pressure from the center of figure. Thus in 

 the experiments, d has been the independent variable, while in the use of the results, « is 

 in general the independent variable. 



For a scjuare plane 90 mm. (3.54 inches) on the side, Kummer obtained the following 

 results, which may be compared with the results given here in chapter Ylll and with the 

 formula of Joessel : 



* Memorial du Genie JIaritime, 1870. 

 t Berlin Akad-Abhandlungen, 1875, 1876. 



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