96 NATURAL SCIENCE [August 
330 of a second. However, a photograph was taken from which it 
has been possible to determine some twenty positions, plotting out a 
whole stroke, with parts of the forward swing on each side (Fig. 6). 
Rough scale of fest , 
ce) ie 2 5 6 Pgs 
Fig. 6. Motion of an Oar during a Stroke. (Boat is moving towards the right{hand. ) 
The camera was fixed about 23 feet above the River Cam when 
there was practically no stream to vitiate the results. The exposures 
were made by a revolving shutter, having three slits, each with an 
angular width of 5° rotating before a slit of about double that 
width. The rotation was maintained by such a weight that the 
speed was fairly uniform during 120 exposures at about 14 
exposures per second. As only 26 of the 120 were used, no 
serious error is introduced by considering the successive photographs 
taken at equal intervals of time. 
Fig. 7. Curves described by points on the Oars. (A), Button; (C), 36’ above 
tip of blade ; (DP), Tip of blade. 
Points were marked on the oar at the button, at 36” above the 
tip of the blade, and at the tip. The motion of these points is re- 
presented by the lines 4, Cand D in Fig. 7. A projecting part of 
