1S98] 



some mom: nit wing experiments 



97 



the bridge from which the photograph was taken necessitated 

 the camera being tilted slightly out of the vertical, so that 

 there is a corresponding change in the scale of the picture 

 in different parts, but as the important part is the loop of 

 the line C, this error is comparatively unimportant. 



In Fig. 8, A repre- 

 sents the locus in space 

 of the turning point 

 determined as the ' en- 

 velope ' of the various 

 oar positions shown on 

 the photograph, show- 

 ing that this point 

 moves outwards from 

 the boat in a convex 

 curve facing the bow 

 of the boat. 



The curve B repre- 

 sents the Instantaneous 

 Centre Locus or point 



Fig. Motion in space of Instantaneous Centre (5) • about which 



and turning 1'oint (A). r 



the oar turns bodily. 



Fig, 9 represents the motion of the Turning Point along the 

 oar. From this it will be seen that, starting from a point some 

 37 inches above the tip, it moves upwards during the first part of the 

 stroke as suggested above, but before the middle of the stroke a 

 curious reaction sets in, and during the rest of the stroke the turn- 

 ing point steadily approaches the tip of the blade, indicating that 

 the blade is coming more and more to rest. 1 



This seems to show that at the be- 

 ginning of the stroke the blade, which 

 is increasing its distance (see curve D, 

 Fig. 7) from the boat's side owing to a 

 diminished obliquity, sets up a swirl 

 which moves backwards in the path of 

 the blade, but forwards between that 

 and the boat. 



During the second half of the stroke 

 the blade enters this forward moving 

 water and has its motion retarded, taking Fig. 9. Position of 'Turning 

 up thereby some of the energy previously Point ' on 0ar durin « the stroke ' 

 imparted to the water. This point requires further experiment. 



1 The meau position is found to be '■><'< inches above the tip, a result coinciding with 

 the rough determination with the Boat eighteen months previously. 



