96 



NATURAL SCIENCE 



[August 



s\o of a second. However, a photograph was taken from which it 

 lias been possible to determine some twenty positions, plotting out a 

 whole stroke, with parts of the forward swing on each side (Fig. 6). 



Rough scaleoffeet 



2 3 t 

 — « i X— 



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. (^4), Button ; (C), 36" above 



tip of blade ; (Z>), 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 A, C and D in Fig. 7. A projecting part of 



