38 PLATEAU ON THE FIGURE OF A LIQUID MASS 
This experiment does not offer any great difficulties; it requires 
however some skill to succeed perfectly *. 
22. In describing ($ 10) the experiment in which the flatten- 
ing of the sphere is effected by the immediate action of the disc, 
I have remarked that the movement of the latter should not be 
continued too long, because the mass of oil then comes to lose 
its form. Now, if we continue, nevertheless, to turn the han- 
dle, with a view to observe the results of this disfigurement, we 
see manifested new and very capricious effects. 
The sphere being well centred with relation to the disc, if we 
give velocities of one turn in six, five or four seconds to the latter, 
we begin, after seven or eight turns, to see the mass of oil elon- 
gate itself horizontally in one direction, taking a form which 
resembles much an ellipsoid of three axes; and, what is more 
singular, this kind of ellipsoid is placed in an eccentric manner 
with relation to the axis of rotation. Figure 4 represents, for a 
Fig. 4. 
velocity of a turn in four seconds, the mass viewed from three 
different sides; that is to say, from above and in the two lateral 
directions of the smallest and of the largest horizontal axis: the 
dotted parts indicate the positions of the disc and of the axis of 
rotation. The aspect of the mass seen from above shows that it 
is slightly bent in one direction; but this effect is evidently 
owing to the resistance of the ambient liquid. 
When once the mass has taken this form, it preserves it in- 
definitely as long as the movement of the disc continues; it con- 
tinues to revolve eccentrically round the latter, and with a ve- 
locity much less than that of this disc. This inferior velocity, 
I may add, evidently also proceeds from the resistance of the 
ambient liquid. 
* On communicating this very experiment to the Academy, in the sitting of 
April 1842 (see the Bulletins), I stated that it was necessary to vary the velo- 
city of rotation. I have since found that having adopted a convenient velocity, 
it was best to keep it uniform. 
