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THE ROYAL SOCIETY OF CANADA 



fitted with a cross-hair which may be moved across the range of view 

 by means of a micrometer screw. The spots focussed by the hollow 

 of each wave are very sharp indeed, so that the centre of each spot 

 can be determined and the distance from one centre to the next 

 measured. 



The velocity and radius of the stream vary slightly throughout 

 the length of the jet, hence the mean radius and the mean velocity 

 were measured for each separate wave, and the surface tension 

 calculated according to formula (3). In this manner the surface 

 tension was determined for each wave in the jet. 



Fig. 8. 



Let Fig. 8 represent a wave from one hollow to the next one. 

 If the arrows represent the direction in which the stream is flowing then 

 the diameter CF will be greater than AD; but since this difference is 

 extremely small the mean of the two (D) is taken and the curve ABC 

 may be considered to have the form of a sine curve. Waves on the 

 surface of a liquid have the form of a trochoid ; but the latter coincides 



