WITHDRAWN FROM THE ACTION OF GRAVIT 243 



stance which is unfavorable to the completion of this realization. We can un- 

 derstand that the relative mobility of the molecules of oil is not sufficiently 

 great to occasion the immediate formation of the liquid layer with that excessive 

 tenuity which is requisite for equilibrium ; the thickness of this layer, although 

 veiy minute, absolutely speaking, is undoubtedly, during the first moments, a 

 considerable multiple of the theoretical thickness. If, then, we produce the 

 layer without extending it to that limit to which it is capable of increasing 

 during the operation, and afterwards leave it to itself, the pressure correspond- 

 ing to its plane svirfaces will still exceed that corresponding to the concave 

 surfaces of the remainder of the liquid system. Hence it follows that the oil 

 within the layer will be driven towards this other part of' the system, and that 

 the thickness of the layer will progressively diminish. The equilibrium of the 

 figure will then be apparent only, and the layer will in realily be the seat of 

 continual movements. The diminution in thickness, however, will be effected 

 slowly, because in so confined a space the movements of the liquid are neces- 

 sarily restrained; this is why, as in the experiment in paragraph 17, the mass 

 only acquires its figure of equilibrium slowly, because there is a cause which 

 impedes the movements of the liquid. The thickness of the layer gradually 

 approximates to the theoretical value, from which the equilibrium of the system 

 would result ; but unfortunately it always happens that before attaining this 

 point the layei» breaks spontaneously. This effect depends, without doubt, 

 upon the internal movements of which I have spoken above. We can imagine, 

 in fact, that when the layer has become of extreme thinness, the slightest cause 

 is sufficient to determine its rupture. The exact figure which corresponds to 

 the equilibrium is therefore a limit towards which the figure produced tends ; 

 this limit the latter approaches very nearly, and would attain if it Avere not itself 

 previously destroyed by an extraneous cause. 



Oiu' experiment has led us to modify the results of theory in one particular 

 instance ; but we now see that, far from weakening the principles of this theory, 

 it furnishes, on the contrary, incomplete as it is, a new and striking verification 

 of it. The conversion of the doubly .concave lens into a system comprising a 

 thin layer is connected with an order of general facts : we shall see that a large 

 number of our liquid figures become transformed, by the gradually produced 

 diminution of the mass of which they are composed, into systems consisting of 

 layers, or into the composition of which layers enter. 



27. If by some modification of our last experiment we could succeed in ob- 

 taining the equilibrium of the liquid system, we might be able to deduce from 

 it a result of great interest — an indication 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 layers ; these might, for 

 instance, then exhibit colors, the tint of which would lead us to this determina- 

 tion. 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 

 efi'ects, 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, 17, 18, and 21, that when a con- 

 tinuous 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 deduce it from theory. We 

 shall do this in the following series, at least on the supposition that the portion 



