36 FLUIDITY AND PLASTICITY

in 1845, he is probably the first to distinguish clearly between
the two regimes.

Hagen (1854) investigated the effect of changes in temperature
upon the rate of efflux in tubes of moderate diameters. Figure 7

0
FIG. 7.-

5 10 15 20 £5 2>0 35 40 f 45 50 55 60 65 10
Temperature Degrees Reaumur

-Transition from linear to turbulent flow. The effect of temperature.

exhibits the results of his experiments. The abscissas are
degrees, Reaumur, the ordinates the volumes in cubic inches
("RheMand Zollen ") transpiring in a unit of time. The pressure
to which each curve corresponds is given at the right of the figure,
being expressed in inches of water. Hagen used three tubes of
varying width as follows: