PROFESSOR E. O. COKER AND MR. S. R. CLEMENT ON THE VARIATION 
(;o 
Critical Velocity. 
It has been pointed out in an earlier section that no attempt was made to deteimine 
the velocity at which stream-line motion broke down, but that the intersections of 
the two sets of lines above and below critical velocity were used to determine the 
minimimi critical velocity. This method of procedure amounts to the deteimination 
of the curve of intersection of two families of straight lines, whose positions aie 
experimentally determined, and it is clear that if the points of intersection lie ujDon 
some straight line in the logarithmic plot, the variation of the critical velocity must 
follow tlie viscosity of the water linearly, while, if they do not, the law cannot be a 
linear one. 
Fig. 4 shows the observations for stream-line flow, and the lines representing eddy 
motion are drawn thereon, and are produced to meet the interpolated lines for 
Critical Velocity. 
RfET PET? SECOND. 
Fig. 6. 
stream-line flow (shown dotted); the points of meeting are found to lie very 
apjiroximately upon the straight line AB. 
It is therefore apparent that these intersections vary as the viscosity, and they 
afford a verification of the formula. 
This is brought out clearly by fig. G, in which the velocities so found are plotted 
directly with resjiect to temperature. As will he seen, less weight is given to tlie 
