618 PLATEAU ON THE PHENOMENA OP A FREE LIQUID MASS 



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 be- 

 come thinner also begins to be developed ; and if the operation 

 is effected too slowly, the system might break before it was com- 

 pleted. When the central mass is sufficiently reduced, and ex- 

 perience 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 phoenomenon, it must 

 be remarked that the intersections of the different 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 effected through the intermedium of minute concave 

 surfaces, and with a little attention we can recognise 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. 1 2 is seen to be reproduced very rapidly. This 

 fact confirms in u 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 py- 

 ramids ; now it also follows, from causes relating to their conti- 



