va PLATEAU ON THE FIGURE OF A LIQUID MASS 
been placed, may be considered as perfectly closed and keeping 
the mixture without evaporation of alcohol. 
In my apparatus the plates of glass are fixed to the metallic 
framing by a resinous cement, and this is slightly attached by 
the alcoholic mixture. It would perhaps be better to use some 
glazier’s putty; for the alcoholic mixture being prepared so as 
not to act any more upon the oil (§§ 6 and 24), this latter 
cement would probably not suffer any alteration. However, the 
resinous mastic resists to such a degree, that I have been able 
to leave the alcoholic liquor, without inconvenience, in the vessel 
for whole months. 
The apparatus which I have just described is the best suited 
for obtaining in all their beauty the phenomena which are the 
object of these experiments; but, as I have said above, a hollow 
sphere of glass of pretty large dimensions might be used with 
less cost and without too much disadvantage, at least for the 
experiments treated of in this part of the memoir. This ought 
to be furnished with two tubular openings, one of which would 
serve for introducing the system of the disc, and the other would 
effect the same object as the second opening of which we have 
spoken above. 
I shall, however, in what follows suppose all along that the 
plane-sided vessel above described is the one employed. 
9. The apparatus being properly arranged, the next thing is 
to operate so as to cause a sphere of oil to surround the disc in 
such a manner that their two centres are sensibly coincident. 
To attain this point, let us first endeavour, before introducing 
the disc into the vessel, to bring the centre of the sphere to re- 
main at the height at which that of the disc should be. It would 
be extremely difficult to accomplish this by suspending a sphere 
in a homogeneous alcoholic mixture, as we have hitherto sup- 
posed: for then there is no reason why the sphere should not 
stand higher or lower ; and if even by chance it were placed ex- 
actly at the desired height, the movements which would be pro- 
duced on introducing the disc would very probably change this 
height. It is therefore necessary to employ a more sure process, 
and the following succeeded perfectly :—We begin by causing 
the alcoholic mixture to contain a small excess of alcohol; then, 
the vessel being furnished with its lid, and the stopper which 
closes the central opening being lifted up, the mixture is intro- 
duced by this opening in such quantity that the vessel be not 
