•WITHDKAWN FROM THE ACTION OF GRAVITY. 



-247 



to be developed in the centre of the figure, (Fig. 14.) This, then, is the defini- 

 tive laminar system to which the liquid cube is reduced by t-he gradual diminu- 

 tion of its mass. 



32. In the preceding experiment, as in that of paragraph 23, the thickness 

 of the layers is at first greater than that which would correspond to equilibrium. 

 If, then, the system were left to itself whilst it still contains a central mass, we 

 should imagine that one portion of the liquid of the layers would be slowly 

 driven towards this mass, and that the layers would gradually become thinner. 

 Moreover, it always happens that one or the other of the latter increases after 

 some time, uudouktedly for the reason which we have already pointed out, 

 (§ 26.) Hence, for the perfect success of the transformation of the cube into 

 the laminar system, one precaution, which has not yet been spoken of, must be 

 attended to. It consists in the circumstance that, from the instant at which 

 the layers arise, the exhaustion of the liquid must be continued as quickly as 

 possible until the central mass has attained a certain degree of minuteness. In 

 fact, as soon as the formation of the layers commences, their tendency to 

 become thinner also begins to be developed ; and if the operation is effected too 

 slowly, the system might break before it was completed. When the central 

 mass is sufficiently reduced — and experience soon teaches us to judge of the 

 suitable point — the action of the syringe must be gradually slackened, and at 

 last the other precautions which we have mentioned must be taken. 



We are able, then, to explain the rupture of the layers so long. as there is a 

 large or small central mass ; but when the laminar system is complete, we do 

 not at the first glance see the reason why the thickness of the layers diminishes, 

 and consequently why destruction of the system takes place. Nevertheless the 

 rupture ultimately takes place in this as in the other case, and the time during 

 which the system persists rarely extends to half an hour. In ascertaining the 

 cause of this phenomenon, it must be remarked that the intersections of the 

 difiereut layers cannot occur suddenly, or be reduced to simple lines : it is 

 evident that the free transition between two liquid surfaces could not be thus 

 established in a discontinuous manner. These transitions must, therefore, be 

 efiected through the intermedium of minute concave surfaces, and with a little 

 attention we can recognize that, in fact, this really takes place. We can then 

 understand that the oil of the layers ought also to be driven towards the places 

 of junction of the latter ; and consequently the absence of the little central 

 mass does not prevent the gradual attenuation of the layers, and the final 

 destruction of the system. 



33. If, during the action of the syringe, when the system shown in Fig. 13 

 has been attained, instead of slowly withdrawing the instrument, it is suddenly 

 detached by a slight shake in a vertical direction, the additional layer is not 

 developed ; but the little mass in Fig. 12 is seen to be reproduced very rapidly^ 

 This fact confirms in a remarkable manner the explanation which we have 

 given in the preceding paragraph. In fact, at the moment at which the point 

 of the instrument is separated from the system, the latter may be considered 

 as composed of hollow pyramids. Now it also follow^s, from causes relating to 



