OF THE CRITICAL VELOCITY OF WATER WITH TEMPERATURE. 
57 
This agreement is shown clearly by fig. 5, where the intersections of the logarithmic 
homologues with the zero ordinate are plotted with reference to the temperature as 
abscissa, and are compared with the intersections determined from the equation 
above, taking the value of jx according to Poiseuille’s formula. At temperatures 
between 5° and 20° C. the agreement is close, the values at 27°'2 and 31° do not 
correspond very well, and there is a very fair agreement at the higher temjDeratures. 
The dotted lines on fig. 4 are the logarithmic homologues at the temperatures of 4°, 
10°‘8, 21°‘2, 30°‘4, 35°, 39° and 50° C. respectively, and these have been interpolated 
by aid of figs. 4 and 5, in order to determine the intersections with the homologues 
for eddy motion also plotted on fig. 4, and which are referred to in the next section. 
The Relation of Slope to Velocity for Water in Eddy Motion. 
A second series of experiments was now commenced with water in eddy motion to 
determine the relation between the loss of head and the velocity at a sufficient 
number of temj^eratures within the range. 
It was extremely difficult to control the temperature, and so no attempt was made 
to obtain a series of runs with temperatures corresponding exactly to those obtained 
TTaipC 5 10 15 ^0 25 50 55 40 45 50 
Fig. 5. 
for stream-line motion, nor was this necessary, as the logarithmic homologuo for 
stream-line motion, corresponding to a similar one for eddy motion, was obtained by 
interpolation from figs. 4 and 5. The observations were made under precisely the 
same conditions as before, except that in the pressure gauge mercury in contact with 
VOL. cci.—A. 
T 
