CHAPTER III
THE AMPLIFICATION OF THE LAW O* POISEUILLE
Tlie Kinetic Energy Correction.—In deriving the law in the
preceding chapter, we limited ourselves to the simplest cstse,
where all of the energy is employed in overcoming viscous resis-
tance -within, the fluid, or p = p,. It is desirable however that
th.e law be given a wider application, and that the law be tested
under the most varied conditions. In the experiments which
Poiseuille used to verify his law, the kinetic energy correction was
negligible, "but the time necessary for a single determination was
often excessive, consuming several hours. It is to be recalled at
this point that in some of his experiments, in which the rate of flow
was higher tlian in the others, the law was not verified. Poise-
uille and others have been greatly troubled in their viscosity de-
terminations by dust particles becoming lodged in the capillary.
If it were possible therefore to employ higher speeds, not only
would "there "be an economy in time but the dust particles would
be much more likely to be swept out from the tube. However
in using these higher velocities a correction for the loss in kinetic
energy must "be applied.
Hagenbach. (1860) is the first one to attempt to make this
correction3 the results of whose work became generally known,
although it appears that Neumann prior to 1860 had made the
correction in nearly its present form. The work of Neumann
wa,s reported by Jacobson in 1860 but his work has also remained
but little "known to workers in this field. Gartenrneister (1890)
reported that Finkener had arrived at a correction which differed
from that of Hagenbach, but Finkener seems not to have pub-
lished, any- monograph on the subject stating why he considered
Ms correction superior. However Couette in the same year
(189O) published a -very important paper in which he arrived
independently at the same correction as that given by Neumann
and Finkener, and a year later Wilberforce (1891) independently
attacked the same subject and showed that there is a slip in the
2 17