Sept. 21, 1888.] 



SCIENTIFIC NEWS. 



313 



SURFACE TENSION. 

 "V 1 7"E here lay before our readers the abstract of a 

 V V paper read before the Microscopical Society of 

 Belgium, as reported in La Nature, from which source we 

 also borrow the accompanying illustrations. 



Fig. 1. 



Let us consider a glass containing water ; is the liquid 

 everywhere constituted alike ? This has been believed 

 or a long time, but the belief is being abandoned. To 

 form a clear idea on this subject, let us examine the 

 forces which act upon the particles. In the first place, 



Fig. 2. 



there is attractive force ; for if we plunge a pencil into 

 the water, and then withdraw it, there will be a drop 

 hanging to the pencil. If we imagine a horizontal plane 

 dividing the drop, all the particles situate above such 

 plane must be regarded as sustained by those which are 

 above, without which there can be no equilibrium. 



This cohesion is evidently due to attractive forces. 

 On the other hand, there are repulsive forces which 

 tend to sever the particles. If we leave the glass of 

 water to itself, the liquid will ultimately entirely evapo- 

 rate. Is not this a proof that if there be forces tend- 



Fig. 3. 



ing to approximate the particles of liquid to each other, 

 there are others in virtue of which these particles 

 diverge from each other ? 



On studying the constitution ot liquids from this 

 point of view we have arrived at the following result : an 



Fig. 4. 



equilibrium cannot exist in a liquid between the 

 attractive and repulsive forces, unless there is, in the 

 immediate proximity to the free surface, a tendency to 

 the mutual separation of particles, combated incessantly 

 by the attractive forces. 



But is not this state of the superficial layer com- 



