AMPLIFICATION OF THE LAW OF POISEUILLE

33

independently but along much the same lines. He tried the
effect of a layer of grease and of silver on the inside of a tube.
He found invariably the same efflux time or even a little greater
which was due to the diminution in the radius of the tube. But
even this latter effect did not occur when the thickness of the
silver layer was a negligible fraction of the radius of the tube.
He then used tubes of white metal, copper, and paraffin using
rates of efflux close to the critical values, and obtained the
following results:

TABLE XL—COUETTE'S EXPEEIMENTS ON SLIPPING

Substance of tube
Temperature
7] Observed
f] Calculated from Poiseuille

CoDDer .....
15 5
0 01175
0 01130

CoDDer ......
17 3
0 01073
0.01079

White metal .....
18 2
0.01037
0.01055

White metal ......
18 9
0.01064
0.01037

White metal ......
18.3
0.01092
0.01052

Paraffin .
12 6
0 01241
0 01219

Paraffin
12 9
0 01278
0.01209

Paraffin ......
12 3
0.01276
0.01228

Couette goes further and gives reasons for the conclusion that

slipping does not occur even after the flow becomes turbulent.

More recently Ladenburg (1908) has carefully repeated the

experiments of Piotrowski under as nearly as possible the same

TABLE XII.—LADENBURG'S EXPERIMENTS WITH AN OSCILLATING GLASS
FLASK, SHOWING ABSENCE OF SLIPPING, AT 19.0°

Flask
Logarithm decrement
Period of vibration
Remark

A ................
0.019570 ±2
11, 973 ±2
Unsilvered

A
0.019642 + 3
12, 049 ±2
Silvered

A ........
0.019620 + 3
11,990±1
Unsilvered

B .......
0.025026 ±25
11,716±4
Unsilvered

B ..............
0.025011 ±15
11, 688 ±2
Silvered

c ................
0.025162 ±2
11,870±2
Silvered