1898] SOME MORE ROWING 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- 
| 
1 
' 
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 & repre- 
sents the Instantaneous 
Centre Locus or point 
in space about which 
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 Pot’ 0 Oar during the Stroke. 
imparted to the water. This point requires further experiment. 
Fig. 8. Motion in space of Instantaneous Centre (6) 
and ‘ Turning Point’ (A). 
1 The mean position is found to be 36 inches above the tip, a result coinciding with 
the rough determination with the float eighteen months previously. 
