AMPLIFICATION OF THE LAW OF POI SEVILLE

23

the actual length of the capillary, which he represents by A. The
corrected viscosity r\Q should therefore be calculated by the
formula

According to Couette the corrected viscosity is always a little
smaller than that calculated by means of Eq. (8) and we obtain
the relation

I

A =1

Since A may be presumed to be the same for tubes of equal
diameter but of unequal lengths I and Z', one should obtain
different viscosities t\ and rjf by applying Eq. (8) to the same fluid.
There would thus be the relation

A =

(11)

To test out his theory, Couette used experimental results of
Poiseuille with tubes A1V and Av which gave poor agreement with
the simple law, Eq. (5) cf. Table II, VII and VIII. The efflux
times are given in column 1, the viscosities yp calculated from
the simple Poiseuille formula (5), in column 2, the more
nearly correct viscosities rj and 77', calculated from Eq. (8) taking
m = 1.00, in column 3.

TABLE VII. — VISCOSITY OF WATEH CALCULATED FROM POISEUILLF/S

EXPERIMENTS WITH TUBE A™
For dimensions cf. Appendix D, Table I, p. 331

Time
r,P Eq. (5)
77 Eq. (8), m = 1.00

8,646
0.01332
0.01328

4,355
0.01349
0.01339

2,194
0.01347
0.01332

1,455
0.01347
0.01324

1,116
0.01355
0.01325

571
0.01384
0.01325

298
0.01443
0.01330