28 Barus and Strouhal— Viscosity of Steel. 
tion at any interface is nowhere sufficient to produce rupture. 
Then that property of a solid in virtue of which it resists very 
small forces (zero-forces) acting through very great intervals of 
time (oo-times) may be termed the viscosity of the solid. That 
property in virtue of which it resists the action of very large 
. forces (co-forces relatively) acting through zero-time may be 
termed the hardness of the solid. Since the application of 
forces in such a way as accurately to meet either of these cases 
is rare, we have in most practical instances mixtures of viscous 
resistances and of hardness to encounter. We may reasonably 
conceive that in the case of viscous motion the molecules slide 
into each other or even partially through each other per inter- 
change of atoms, so that the molecular configuration is being 
continually reconstructed ; that in the other case (hardness) the 
molecules are urged over and across each other and that there- 
fore the intensity of cohesion is in this case more or less 
thoroughly impaired. The interpenetration of the molecules cf 
a viscous substance is necessarily favored by temperature. 
Hence we infer the experimental result that the viscous influ- 
ence of temperature is marked. If Clausius’s theory of elec- 
trolysis be correct, then a certain instability or imperfect uni- 
formity in the molecular structure of solids follows at once 
from the fact that many solids, notably glass,* may be electro- 
lyzed even at moderately high temperatures (300°). 
4. The stored torsional stress imparts a strain to the solid. 
Viscous detorsion therefore is accompanied by a residual phe- 
nomenon. The observed deforination will continue until the 
applied tendency to change of form is reduced in value to the 
evoked and increasing tendency against change of form. If 
the applied stress be removed, the reciprocating stress becomes 
apparent and produces viscous effects of its own kind, as Kohl- 
rausch has shown. ‘The result has many magnetic and electri- 
eal analogies, among which the phenomenon ‘of residual static 
charge is most obvious. In the tubular apparatus (table 31), 
the residual deformation of the preceding twist may be super- 
imposed on the deformation immediately in progress. Whether 
the two residual phenomena here annul each other so that the 
primary detorsion is alone exhibited remains to be seen. 
In liquids there is no such reaction unless it be the recipro- 
cating force of galvanic polarization. In polarization, how- 
ever, the mechanism is of an obviously chemical kind. In 
solids it is believed to be not chemical. 
Sectional areas of bifilar wires.—The essential peculiarity of 
the bifilar apparatus is this, that the two wires are twisted by 
3 Warburg: Wied. Ann., xxi, p. 622, 1884. literary notes are there given. 
Warburg is able to replace $ 8 of the sodium of glass by sodium of the anode. 
