FREED FROM THE ACTION OF GRAVITY. 29 
and thence decreases rapidly in the rest of this body. Now, at 
the first moment of the formation of the ring of oil, we have 
seen ($ 12) that the latter remains united to the disc by a thin 
film of the same liquid, and we may convince ourselves that this 
film exerts, on the inner circumference of the ring, a consider- 
able force of traction. In fact, if we stop the movement of the 
disc a little too soon, that is to say a little before the ring has 
reached its maximum of diameter, the film of oil does not break, 
and the ring then returns upon itself (§ 11) with a much greater 
rapidity than when the film of oil is broken, and the ring re- 
mains isolated. The traction which the film of oil exerts on the 
inner circumference of the ring ought therefore to produce an 
effect analogous to that of the attraction of Saturn, that is to 
say, contribute to increase the flattening. Well, the ring of oil 
before the rupture of the film presents a very marked flattening. 
In order to obtain it perfectly, care must be taken that the 
sphere be well centred in relation to the disc, before beginning 
the experiment; and it is useful to turn the handle with a velo- 
city somewhat less than that indicated at § 11: the most suit- 
able velocity has appeared to me to be about two turns in a 
second. As soon as the film of oil breaks the flattening disap- 
pears, and the generatrix of the ring becomes, as we have seen, 
sensibly circular*, 
* Thad thought that it would be possible to obtain rings isolated and greatly 
flattened by operating upon larger masses of oil; for then the ring having a 
larger volume, the influence of the molecular attraction should be less. But I 
have found, that in operating on larger masses it was necessary, in order to ob- 
tain the ring in a regular manner, to employ a more feeble velocity of rotation ; 
so that if the influence of the molecular attraction was diminished, that of the 
centrifugal force was so equally. The flattening then did not become more 
sensible, or if I have sometimes imagined that I observed any, I have not been 
able to reproduce it at will. I have operated thus on spheres which were suc- 
cessively about 10, 11, 12 and 14 centimetres in diameter, with discs of a dia- 
meter of from 7 to 9 centimetres, and in a vessel with plane surfaces, having a 
bottom 85 centimetres square, and a depth of 25 centimetres. The effects, 
however, thus obtained are very beautiful; the rings are magnificent, present 
a considerable diameter, and remain sometimes for eight to ten seconds before 
returning on themselves. With a sphere of 10 centimetres diameter, a disc of 
7, and a velocity a little less than oue turn of the disc per second, we obtain, 
in a very beautiful and very marked manner, the flattening resulting from the 
traction of the film of oil. 
These experiments however are inconvenient and difficult, on account of the 
2 
_ large dimensions of the vessel, and the great quantity of alcoholic liquid neces- 
sary to fill it. 
It may be conceived, moreover, why a larger mass of oil requires a less ve- 
locity of rotation to produce a regular ring. It is precisely because the mole- 
cular attraction has less influence; whence it results that, if we attempt to em- 
