98 NATURAL SCIENCE [August 
In order to determine the efficiency of propulsion it is only 
necessary to find what proportion of the whole work done is 
developed as kinetic energy in the water. If the whole pressure 
of the blade against the water be P, while the centre of pressure 
moves through a distance a perpendicular to the blade, the kinetic 
energy delivered to the water is Pa. For every small angle @ through 
which the blade turns while the turning point is at a distance 
from the centre of pressure, the above product = Px. 
Without entering into details the angles between successive 
positions of the oar, given in Fig. 6, were measured and corrected 
by interpolation from a curve, while corresponding values of x and 
P were found from Fig. 9 and C of Fig. 4 respectively.” 
In this way it was found that almost exactly 4 (33°4 per cent.) 
of the work was left behind in the water as kinetic energy set up 
by the oar, giving an efficiency of 66°6 per cent. This efficiency 
coefficient is concerned, of course, only with the rowing mechanism, 
and takes no account of physiological waste of energy. 
Fig. 10. Fatigue Effect. .4, Work ; 2, Greatest Pull; C, Change in Form. 
The mechanical efficiency is increased by increasing the size of 
the blade, so that it can react on a larger body of water, and by in- 
creasing the length of the oar, both inboard and outboard, in order 
to diminish the obliquity at the ends of the stroke. This theoretical 
possibility is hampered by practical considerations until boatbuilders 
1 See Appendix II. 
2 C unfortunately was not the oarsman who was rowing in the oar experiment, but, 
for a general result, this is of no very great moment, 
