34 PLATEAU ON THE FIGURE OF A LIQUID MASS 
formed by the return of the ring upon itself, continues still to 
revolve for some time, completely isolated in the ambient liquid. 
Its figure is then, as well as the eye can judge of it, a perfect 
ellipsoid of revolution, which gradually approximates to a sphere 
in proportion as the rotatory motion becomes weaker *. Thus 
* T had expected to be able to obtain a revolving isolated mass by means of 
another process, viz. by forming a sphere of oil in the middle of a cylindrical 
flask so arranged as to be able to turn upon its axis; then causing this flask 
thus to turn with rapidity, until all the liquid within, alcoholic mixture and 
mass of oil, had taken the same motion ; then suddenly stopping the flask. In 
effect, it seems that then the alcoholic liquor being the first to lose its rotatory ~ 
motion by the friction against the stationary sides of the flask, a moment 
must occur when the mass of oil maintains an excess of angular velocity over 
the ambient liquid, and that then the effects of centrifugal force upon that mass 
may manifest themselves. But the experiment gives few results. First, it is 
extremely difficult to keep a mass of oil in the middle of the flask. We keep 
it tolerably in the axis of the latter, because, if we have succeeded in placing 
it so that its centre is little removed from that axis, the rotation of the am- 
bient liquid brings it there, and then retains it there very well. But it is not 
the same in the direction of the height of the flask. If a homogeneous alcoholic 
mixture be employed, and the sphere of oil is placed, before turning the flask, 
a little higher or lower than the middle of the height of the latter, it quits 
its place when the flask turns, to ascend, in the first case, or to descend, 
in the second, until it comes to be dispersed against one of the two bases of 
the flask. This effect is attributable, I think, to the fact that the two bases 
exercising upon the sections of liquid which touch them a motive action much 
greater than that to which the parallel sections of the interior of the mass are 
subjected, there ensues near these bases, at the commencement of the rotation, 
an excess of centrifugal force, which determines a tendency upwards and down- 
wards of the liquid near the axis. It is therefore necessary to endeavour to 
place the sphere of oil in a position very near to the middle of the height of 
the vessel. Unfortunately we cannot use for this purpose the process of su- 
perposition of the alcoholic layers of unequal density (§ 9); for then, in the 
rotation of the flask, the denser inferior layers come necessarily, by the excess 
of centrifugal force which results from their excess of density, to rise against 
the sides, causing the less dense liquid to occupy the axis; and in this move- 
ment the mass of oil is drawn downwards, and is also dispersed upon the 
bottom of the vessel. 
By employing a homogeneous alcoholic mixture and a sphere of oil of only 
about three centimetres diameter, I however succeeded several times, by dint of 
patience, in giving to this sphere a sufficiently exact position in the flask to be 
able to keep it at the same height until it had itself taken the rotatory move- 
ment of the whole system. But then, when I stopped the flask, a violent in- 
ternal agitation was produced, which almost always dispersed the oil in innu- 
merable spherules throughout the alcoholic liquid, or at least destroyed its form 
in a completely irregular manner. I attribute these effects to the following 
cause. When the flask is stopt, the portions of the alcoholic liquid which touch 
the sides and bases, losing first their centrifugal force, the more internal por- 
tions, which still retain theirs, make their way through them, dividing them, 
and this confusion is soon propagated to the axis, where it gives rise either to 
the dispersion or to the irregular disfiguring of the mass of oil. 
In the cases in which I have been able to give a suitable position to the 
sphere of oil, I have observed a curious effect ; namely, that in the first instants 
of the rotation of the vessel the mass of oil quits the spherical form, and be- 
comes elongated in the direction of the axis of rotation, This elongation is 
