WITHDRAWN PROM THE ACTION OF GRAVITY. 613 



might be able to deduce from it a result of great interest — an in- 

 dication of the value of the radius of the sphere of activity of the 

 molecular attraction. In fact, we might perhaps find out some 

 method of determining the thickness of the layer ; these might, 

 for instance, then exhibit colours, the tint of which would lead 

 us to this determination. Now we have seen that in the state 

 of equilibrium of the figures, half the thickness of the layer 

 would be less than the radius in question ; hence we should then 

 have a limit above which the value of this same radius would 

 exist. In other words, we should know that the molecular 

 attraction produces sensible effects, even at a distance from its 

 centre of action beyond this limit. Our experiment, although 

 insufficient, may thus be considered as the first step towards the 

 determination of the distance of sensible activity of the molecular 

 attraction, of which distance at present we know nothing, except 

 that it is of extreme minuteness. 



;: 28. Let us now return to the consideration of thick masses. 

 It follows from the experiments related in paragraphs 13, 14, 

 17j 18 and 21, that M'hen a continuous portion of the surface 

 of such a mass rests upon a circular periphery, this surface is 

 always either of spherical curvature or plane. But to admit 

 this principle in all its generality, we must be able to de- 

 duce it from theory. We shall do this in the following series, 

 at least on the supposition that the portion of the surface in 

 question is a surface of revolution. We shall then see that this 

 same principle is of great importance. We may remark here, 

 that in the experiment in paragraph 23, the layer commences 

 to appear as soon as the surfaces can no longer constitute 

 spherical segments. Now we shall again find, that in the other 

 cases, when a full figure is converted, by the gradual withdrawal 

 of the liquid, into a system composed of layers, or into the com- 

 position of which layers enter, the latter begin to be formed when 

 the figure of equilibrium, which the ordinary law of pressures 

 jvpould determine, ceases to be possible. The mass then assumes, 

 ior tends to assume, another figure, compatible with a modifica- 

 ftion of this law. Such is the general principle of the formation 

 pf layers under the circumstances in question. 



29. After having formed a converging and a diverging liquid 

 lens, it appeared to me curious to combine these two kinds of 

 lens so as to form a liquid telescope. For this purpose, I first 

 substituted for the ring of iron wire in paragraph 18 a circular 



