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Mr. W. Ellis Williams on the 



value has therefore been passed. It will be noticed that the 

 form of the stream-lines has changed slightly. The diagram 

 is no longer symmetrical about the median plane, but the 

 point of zero velocity and the stream-lines which centre on it 

 have moved so as to be behind the centre of the sphere. 

 The velocity in front of the sphere is accordingly diminished 

 .and that behind it increased. The change is much more 

 marked in fig. 5, Photo (PI. IX.), which corresponds to a 

 velocity of *38 cm. per sec. in the same mixture. 



Sphere in glycerine, Ya/v=3'7 (Experimental). 



Va/v is now 3*7, and it will be seen that the point of zero 

 velocity has moved still further back and that the stream-lines 

 around it are somewhat elongated instead of being approxi- 

 mately circular as in the previous diagrams. 



Fijr. G. 



Sphere in water, Va/*»=23 (Experimental). 



In fig. 6, Photo D (PI. IX.) we get the first of the results 

 for water. The velocity is *24 cm. per sec, and the value 



