602 PLATEAU ON THE PH.ENOMENA OF A FREE LIQUID MASS 



compels the liquid to pass through the aperture in the plate; 

 and the phaenomenon must necessarily result, either from a 

 pressure exerted by that portion of the superficial layer which 

 belongs to the most convex segment, or by a traction produced 

 by the portion of this same layer belonging to the other segment. 

 Our experiment not being alone capable of determining our 

 choice between these two methods of explaining the effect in 

 question, let us provisionally adopt the first, i. e. that which 

 attributes it to pressure. In our experiment, this pressure ema- 

 nates from the superficial layer of the most curved segment ; but 

 it is easy to see that the superficial layer of the other segment 

 also exerts a pressure which, alone, is less than the preceding. 

 In fact, if for the most curved segment a segment less curved 

 than the other were substituted, the oil would then be driven 

 in the opposite direction. Hence it follows that the en- 

 tire superficial layer of the mass exerts a pressure upon the 

 liquid which it encloses, and that the intensity of this pressure 

 depends upon the curvatures of the free surface. Moreover, as 

 the liquid proceeds from the most curved segment to that 

 which is least so, it is evident that in the case of a convex sur- 

 face, the curvature of which is spherical, the pressure is greater 

 in proportion as the curvature is more marked, or as the radius 

 of the sphere to which the surface belongs is smaller. Lastly, 

 since a plane surface may be considered as belonging to a sphere, 

 the radius of which is infinitely great, it is evident that the 

 pressure corresponding to a convex surface, the curvature of 

 which is spherical, is superior to that which would correspond 

 to a plane surface. All ihese results were announced by theory. 

 They perfectly verify then that part of the latter to which they 

 refer, and this concordance ought now to decide in favour of the 

 hypothesis of pressure. This same part of the theory was already 

 verified, i-n its application to liquids submitted to the action of 

 gravity, by the phaenomenon of the depression presented by 

 liquids in capillary tubes, the walls of which they do not moisten ; 

 but the series of our experiments, setting out with the elements 

 of the theory, and following it step by step, yields far more direct 

 and complete verification. Our last experiment leads us to still 

 further consequences. The liquid passing from one of its segments 

 to the other, so long as their curvatures have not become iden- 

 tical, and the pressures corresponding to the two portions of the 

 superficial layer becoming equal to each other simultaneously 



