122 
Lord Kelvin on the Motion of a Liquid. 
SESS. 
liquid and air were infinitely small, he may be incredulous unless 
he tends to have faith in all assertions made in the name of 
science. 
(3) If the boundary is an enclosing vessel of any real material 
(and therefore neither perfectly rigid nor perfectly elastic), and if it 
is laid on a table and left to itself, under the influence of gravity, 
the liquid, supposed perfectly inviscicl, will lose energy continually 
by generation of heat in the containing vessel, and will come 
asymptotically to rest in the configuration of stable equilibrium with 
surfaces of equal density horizontal and increasing density down- 
wards. 
(4) With other conditions as in (3), but no gravity, the ultimate 
configuration of rest will be infinitely fine mixture (probably, I 
think of equal density throughout). Consider, for example, two 
homogeneous liquids of different densities filling the closed vessel, 
or a single homogeneous liquid not filling it. As an illustration, 
take a bottle half full of water, and shake it violently. Observe 
how you get the whole bottle full of a mixture of fine bubbles 
of air, nearly homogeneous throughout. Think what the result 
would be if there were no gravity, and if the water and air were 
inviscid and the bottle shaken as gently as you please ; and if 
there were perfect vacuum in place of the air ; or, if for air were 
substituted any liquid of density different from that of water. 
